G20801OO(JUN-048-PCT)_Eng. Spec_Final.doc ABSORBENT ARTICLE TECHNICAL FIELD [0001] The present invention relates to an absorbent article such as a diaper. BACKGROUND ART [0002] Diapers each including an absorbent body composed of a liquid-permeable topsheet, a liquid-impermeable backsheet, and an absorber have been widely known (Patent Literature 1, for example). [0003] Specifically, as shown in Fig. 1, a diaper 100 includes an absorbent body 101 composed of a liquid-permeable topsheet 101a, a liquid-impermeable backsheet 101 b, and an absorber 101 c disposed between the topsheet 101a and the backsheet 101b. The absorber 101c absorbs liquid and retains the liquid. [0004] The absorbent body 101 extends across a back-side region S1, a crotch region S2, and a front-side region S3 arranged in a longitudinal direction L from a back side Ba to a front side Fr. The absorbent body 101 covers a wearer from the back side Ba to the front side Fr with the crotch of the wearer being centered. On both sides of the absorbent body 101 in a width direction W, paired right and left side flap portions 110 are provided. The side flap portions 110 are formed by extending the topsheet and backsheet 101a and 101 b. The width direction W of the absorbent body 101 refers to a direction orthogonal to the longitudinal direction L from the back side Ba to the front side Fr in a plan view of the diaper 100. Each of the side flap portions 110 includes elastic members 120 extended in the longitudinal direction L. [0005] The pair of elastic members 120 are provided in the longitudinal direction L of the absorbent body 101 in a curved fashion not in a straight fashion. The distance between the pair of elastic members 120 is therefore set wider in the front-side region S3 than in the back-side region S1. [0006] In this conventional example, the diaper 100 can be fit along groin part of a wearer when the wearer wears the diaper 100 and provide excellent wearability. Moreover, space is formed between the diaper 100 and the wearer on the front side Fr and can temporarily hold urine. Leakage of urine can be prevented as much as possible. [0007] Another conventional diaper of this kind is disclosed in Patent Literature 2. Specifically, as shown in Fig. 2, a diaper 100A includes an absorbent body 101A composed of a liquid-permeable topsheet 101d, a liquid-impermeable backsheet 101e, and an absorber 101f disposed between the topsheet 1 G20801OO(JUN-048-PCT)_Eng. SpecFinal.doc 101d and backsheet 101e in a similar manner to the diaper 100. [0008] The configuration of the diaper 100A differs from that of the diaper 100 in that the distance between the paired elastic members 120A is set wider in the back-side region S1 than in the front-side region S3. [0009] In this conventional example, the diaper 100A can be fit to wrap around the hips of the wearer, thus providing excellent wearability. Patent Literature 1: Japanese Patent Laid-open Publication No. 11-47189 (Pages 2 to 3, Fig. 1) Patent Literature 2: Japanese Patent Laid-open Publication No. 10-243961 (Page 3, Fig. 1) DISCLOSURE OF THE INVENTION [0010] However, in the conventional diaper 100 (diaper 1O0A), the paired right and left elastic members 120 (elastic members 120A) are curved so that the distance therebetween varies among the back-side, crotch, and front-side regions S1 to S3. It is therefore necessary to cut the topsheet 101a (topsheet 101d) and backsheet 101b (backsheet 101e) in a curve to form side flap portions 110 (side flap portions l1A). Cutting the topsheet 101a (topsheet 1Old) and backsheet 101b (backsheet 1Ole) in a curve causes waste of materials. [0011] Moreover, since the elastic members 120 (elastic members 120A) are placed in a curved fashion, processing thereof is complicated. [0012] An object of the present invention is to provide an absorbent article capable of fitting to a wearer and being manufactured using less materials and easier processing for manufacturing. [0013] An aspect of the present invention is an absorbent article (a diaper 1A, for example) including: an absorbent body (absorbent body 2) which includes at least a liquid-permeable topsheet (topsheet 3), a liquid-impermeable backsheet (backsheet 4), and an absorber (absorber 5) disposed between the topsheet and the backsheet and configured to absorb and retain liquid, the absorbent body having a back-side region (back-side region Si), a crotch region (crotch region S2), and a front-side region (front-side region S3) located in a longitudinal direction L from a back side Ba to a front side Fr when the absorbent article is wom; and a pair of right and left side flap portions (side flap portions 10) provided on both sides of the absorbent body in a width direction W, in which a front-side stretched region (front-side stretched region 15) which is stretched in a waistline direction (width direction W) is provided in each of the side flap portions in the front-side region. [0014] According to such an aspect, when a wearer wears the absorbent article, the waistline dimension of 2 G20801OO(JUN-048-PCT)_ Eng. Spec_Final.doc the absorbent body and the pair of side flap portions is larger than the other place due to the front-side stretched region. Accordingly, the absorbent article can be fit along the wearer's groin portion when the wearer wears the absorbent article. [0015] Accordingly, the absorbent article is excellent in wearability. Moreover, the absorbent article forms a space between the wearer and the absorbent body and pair of side flap portions on the front-side Fr and can temporarily hold urine, thus being prevented from leaking urine as much as possible. The front-side stretched regions are formed by partially stretching the pair of side flap portions. Accordingly, it is unnecessary to make each side flap portion larger on the front side Fr than the other part, or in other words, it is unnecessary to provide edges of the side flap portions in the waistline direction in a curved fashion on the front side Fr. In the absorbent article capable of fitting along the wearer's groin part when the wearer wears the absorbent article and forming a space between the wearer and the absorbent article on the front side Fr, it is possible to reduce use material, facilitate processing, and achieve lower cost accordingly. [0016] Another aspect of the present invention is an absorbent article (diaper 1 E, for example), including: an absorbent body (absorbent body 5) which includes at least a liquid-permeable topsheet (topsheet 3), a liquid-impermeable backsheet (backsheet), and an absorber (absorber 5) disposed between the topsheet and the backsheet and configured to absorb and retain liquid, the absorbent body having a back-side region (back-side region SI), a crotch region (crotch region S2), and a front-side region (front-side region S3) located in a longitudinal direction from a back side Ba to a front side Fr when the absorbent article is wom; and a pair of right and left side flap portions (side flap portions 10) provided on both sides of the absorbent body in a width direction, in which a back-side stretched region (back-side stretched region 14) which is stretched in a waistline direction (width direction W) is provided in the back-side region of each of the side flap portions. [0017] According to the above aspect, when the wearer wears the absorbent article, the dimension of the waistline width of the pair of side flap portions is extended by the back-side stretched regions. Accordingly, the absorbent article can be fit so that the absorbent body and the pair of side flap portions wrap around the hips, thus providing excellent wearability. Moreover, the absorbent article can form a space between the wearer and the absorbent body while wrapping around the hips with the absorbent body and the pair of side flap portions on the back side Ba. The absorbent article therefore can temporarily hold excretion in the space, thus being prevented from leaking excretion as much as possible. The back-side stretched regions are formed by partially stretching the pair of side flap portions. Accordingly, it is unnecessary to make each side flap portion larger on the back side Ba than the other part, or in other words, it is unnecessary to provide edges of the side flap portions in the waistline direction in a curved fashion on the back side Ba. In the absorbent article capable of fitting to a wearer so as to wrap around his/her hips, it is possible to reduce use material, facilitate processing, and achieve lower cost accordingly. [0018] 3 G2080100(JUN-048-PCT)_Eng. SpecFinal.doc According to the present invention, in an absorbent article capable of fitting to a wearer, it is possible to achieve reduction in use material, facilitated processing at manufacturing, and the like. BRIEF DESCRIPTION OF DRAWINGS [0019] [Fig. 1] Fig. 1 is a plan view showing a developed state of a conventional diaper. [Fig. 2] Fig. 2 is a plan view showing a developed state of another conventional diaper. [Fig. 3] Fig. 3 is a plan view showing a developed state of diaper according to Embodiment 1-1 of the present invention. [Fig. 4] Fig. 4 is a cross-sectional view of the diaper (Fig. 3) according to Embodiment 1-1 of the present invention taken along a line A-A. [Fig. 5] Fig. 5 is a cross-sectional view of the diaper (Fig. 3) according to Embodiment 1-1 of the present invention taken along a line B-B. [Fig. 6] Fig. 6 is a cross-sectional view of the diaper according to Embodiment 1-1 of the present invention in use taken along the line B-B. [Fig. 7] Fig. 7 is a plan view showing a developed state of the diaper according to Embodiment 1-1 of the present invention in use. [Fig. 8] Fig. 8 is a cross-sectional view of a main portion of a stretching apparatus manufacturing the diaper according to Embodiment 1-1 of the present invention. [Fig. 9] Fig. 9 is a plan view of a diaper according to Embodiment 1-2 of the present invention. [Fig. 10] Fig. 10 is a cross-sectional view of a diaper according to Embodiment 1-3 of the present invention. [Fig. 11] Fig. 11 is a cross-sectional view of a diaper according to Embodiment 1-4 of the present invention. [Fig. 12] Fig. 12 is a plan view of a developed state of a diaper according to Embodiment 1-5 of the present invention. [Fig. 13] Fig. 13 is a cross-sectional view of the diaper according to Embodiment 1-5 of the present invention taken along a line C-C. [Fig. 14] Fig. 14 is a cross-sectional view of the diaper according to Embodiment 1-5 of the present invention taken along a line D-D. [Fig. 15] Fig. 15 is a cross-sectional view of the diaper in use according to Embodiment 1-5 of the present invention taken along the line D-D of Fig. 12. [Fig. 16] Fig. 16 is a plan view showing a developed state of the diaper according to Embodiment 1-5 of the present invention in use. [Fig. 17] Fig. 17 is a plan view of a diaper according to Embodiment 1-6 of the present invention. [Fig. 18] Fig. 18 is a plan view of a diaper according to Embodiment 1-7 of the present invention. [Fig. 19] Fig. 19 is a cross-sectional view of a diaper according to Embodiment 1-8 of the present invention, showing a developed state. [Fig. 20] Fig. 20 is a cross-sectional view of a diaper according to Embodiment 1-9 of the present invention, showing a developed state. [Fig. 21] Fig. 21 is a cross-sectional view of a diaper according to Embodiment 2-1 of the present invention. [Fig. 22] Fig. 22 is a plan view of a developed state of a diaper according to Embodiment 2-2 of the present invention. 4 G2080100(JUN-048-PCT)_Eng. Spec_Final.doc [Fig. 23] Fig. 23 is a cross-sectional view of Fig. 22 taken along a line Al-Al. [Fig. 24] Fig. 24 is a cross-sectional view of Fig. 22 taken along a line B1 -B1. [Fig. 25] Fig. 25 is a plan view of a diaper, showing a distance with the permeability increased. [Fig. 26] Fig. 26 is a plan view of a diaper, showing a distance with the permeability increased. [Fig. 27] Fig. 27 is a cross-sectional view of a stretching apparatus. [Fig. 28] Fig. 28 is a cross-sectional view of a diaper according to Embodiment 2-3 of the present invention. [Fig. 29] Fig. 29 is a cross-sectional view of a diaper according to Embodiment 2-4 of the present invention. [Fig. 30] Fig. 30 is a cross-sectional view of a diaper according to Embodiment 2-5 of the present invention [Fig. 31] Fig. 31 is a plan view of a diaper according to Embodiment 2-6 of the present invention. [Fig. 32] Fig. 32(a) is a perspective view of a diaper of a conventional example, and Fig. 32 (b) is a plan view of a developed state of a diaper of another conventional example. [Fig. 33] Fig. 33 shows a diaper according to Embodiment 3-1 of the present invention, which is a plan view of the developed state of the diaper. [Fig. 34] Fig. 34 shows a diaper according to Embodiment 3-1 of the present invention, which is a cross-sectional view of Fig. 33 taken along a line A2-A2. [Fig. 35] Fig. 35 shows a diaper according to Embodiment 3-1 of the present invention, which is a cross-sectional view of Fig. 33 taken along a line B2-B2. [Fig. 36] Fig. 36 shows a diaper according to Embodiment 3-1 of the present invention, which is a cross-sectional view of Fig. 33 taken along the line B2-B2 when the diaper is in use. [Fig. 37] Fig. 37 is a cross-sectional view of a main portion of a stretching apparatus. [Fig. 38] Fig. 38 shows a diaper according to Embodiment 3-1 of the present invention, (a) being a plan view with the crotch region of a side flap portion not pulled outward at the center, (b) being a plan view with a central edge of the crotch region of the side flap portion being pulled outward. [Fig. 39] Fig. 39 is a cross-sectional view of a diaper according to Embodiment 3-2 of the present invention. [Fig. 40] Fig. 40 is a cross-sectional view of a diaper according to Embodiment 3-3 of the present invention. [Fig. 41] Fig. 41 is a plan view of a developed state of a diaper according to Embodiment 3-4 of the present invention. [Fig. 42] Fig. 42 is a plan view of a developed state of a diaper according to Embodiment 3-5 of the present invention. [Fig. 43] Fig. 43 is a plan view of a diaper of a conventional example. [Fig. 44] Fig. 44 shows Embodiment 4-1 of the present invention, which is a plan view of a developed state of a diaper. [Fig. 45] Fig. 45 shows Embodiment 4-1 of the present invention and is a cross-sectional view of Fig. 44 taken along a line A-A. [Fig. 46] Fig. 46 shows Embodiment 4-1 of the present invention which is a cross-sectional view of Fig. 44 taken along a line B-B. [Fig. 47] Fig. 47 shows Embodiment 4-1 of the present invention, which is a cross-sectional view of Fig. 44 taken along a line C-C. [Fig. 48] Fig. 48 shows Embodiment 4-1 of the present invention, which is a plan view showing a 5 G20801OO(JUN-048-PCT)_Eng. SpecFinal.doc developed state of a diaper in use. [Fig. 49] Fig. 49 shows Embodiment 4-1 of the present invention, which is a cross-sectional view of a stretching apparatus. [Fig. 50] Fig. 50 shows Embodiment 4-1 of the present invention, which is a side view of a diaper in use. [Fig. 51] Fig. 51 shows Embodiment 4-2 of the present invention, (a) being a plan view of a diaper before use, (b) being a plan view of the diaper in use. [Fig. 52] Fig. 52 shows Embodiment 4-3 of the present invention, (a) being a plan view of a diaper before use, (b) being a plan view of the diaper in use. [Fig. 53] Fig. 53 shows Embodiment 4-4 of the present invention, which is a plan view of a developed state of a diaper. MODES FOR CARRYING OUT THE INVENTION [0020] Next, embodiments of the present invention are described. In the following description, same or similar portions are given same or similar reference numerals. It should be noted that the drawings are schematic and ratios of dimensions and the like are different from actual ones. [0021] Accordingly, specific dimensions and the like should be determined in consideration of the following description. Moreover, the drawings also include portions having different dimensional relationships and ratios from each other. [0022] Figs. 3 to 7 show a diaper 1A according to Embodiment 1-1 of the present invention. Fig. 3 shows a plan view of a developed state of the diaper. Fig. 4 shows a cross-sectional view of Fig. 1 taken along a line A-A. Fig. 5 is a cross-sectional view of Fig. 3 taken along a line B-B. Fig. 6 shows a cross-sectional view of the diaper in use. Fig. 7 is a developed plan view showing the diaper in use. [0023] As shown in Fig. 3, in the diaper 1A, a back side Ba and a front side Fr are determined, and a back-side region S1, a crotch region S2, and a front-side region S3 are sequentially provided in a longitudinal direction L from the back side Ba to the front side Fr. [0024] As shown in Figs. 3 to 5, the diaper 1A as an absorbent article includes an absorbent body 2, a pair of right and left side flap portions 10 provided on both sides of the absorbent body 2 in a width direction W, a pair of back-side waist flap portions 20, and a pair of front-side waist flap portions 21. [0025] Specifically, the back-side waist flap portions 20 are provided on both ends of the pair of side flap portions 10 in the width direction W on the back side Ba. The front-side waist flap portions 21 are provided on both ends of the pair of side flap portions 10 in the width direction W on the front side Fr. 6 G20801OO(JUN-048-PCT)_Eng. Spec_Final.doc [0026] The absorbent body 2 includes at least a liquid-permeable topsheet 3, a liquid-impermeable backsheet 4, and an absorber 5 disposed between the topsheet 3 and backsheet 4 and configured to absorb and retain liquid. The absorbent body 2 extends across the back-side region S1, crotch region S2, and front-side region S3 in the longitudinal direction from the back side Ba to the front side Fr. The absorbent body 2 covers the wearer at the back side Ba, crotch side, and front side Fr. [0027] The both edges of the topsheet 3 in the width direction W are folded so as to wrap around the absorber 5. The folded portions of the topsheet 3 and the absorber 5 are bonded to the backsheet 4 with glue such as a hot melt adhesive. The topsheet 3 is made of hydrophilic nonwoven fabric, woven fabric, perforated plastic film, perforated hydrophobic nonwoven fabric, laminated nonwoven fabric manufactured by spunbond/meltblown/spunbond (hereinafter, referred to as SMS) with a basis weight of 10 g/m 2 , or the like. [0028] The backsheet 4 is made of non-breathable film with a basis weight of 23.5 g/cm 2 . The backsheet 4 may be made of moisture-permeable or moisture-impermeable film, a sheet composed of such permeable or impermeable film bonded to nonwoven fabric, or the like. [0029] The absorber 5 is a laminate having liquid absorption and retention characteristics. Specifically, the absorber 5 is formed by mixing absorbent pulp and a highly absorbent polymer. [0030] The pair of side flap portions 10 are composed of the portions of the backsheet 4 extended on both sides of the absorbent body 2 in the width direction W and the portions of a liquid-impermeable exterior sheet 11 laid on the rear surface of the absorbent body 2 and the backsheet 4. The backsheet 4 and exterior sheet 11 are bonded with glue such as a hot melt adhesive. The exterior sheet 11 is formed so as to be longer in the width direction W than the backsheet 4. [0031] In each side flap portion 10, four elastic members 12a to 12d extended in the longitudinal direction L are provided in the crotch region S2 and part of the back and front-side regions S1 and S3 with the crotch region S2 being centered. [0032] The outer three elastic members 12a to 12c are provided on each side of the exterior sheet 11, which is longer in the width direction W than the backsheet 4. The elastic member 12d located at the innermost position is disposed at substantially the center between the side edge of the absorbent body 2 and the elastic member 12a located at the outermost position. The elastic member 12d is provided between the exterior sheet 11 and backsheet 4. Each of the elastic members 12a to 12d is made of polyurethane elastic yam, for example. 7 G2080100(JUN-048-PCT)_Eng. SpecFinal.doc [0033] In each side flap portion 10, a front-side stretched region 15 stretched in a waistline direction (in the width direction W) is provided between the absorbent body 2 and the elastic member 12a located at the outermost position in the front-side region S3. Specifically, each front-side stretched region 15 is provided between the side edge of the absorbent body 2 and the vicinity of the inside of the elastic member 12c, which is located closest to the absorbent body 2 among the outer three elastic members 12a to 12c provided in the side flap portion 10. [0034] Each front-side stretched region 15 is a region formed by stretching processing so as to have a lower basis weight than the other region. In the front-side stretched region 15, dense portions (no referential numbers) stretched a small amount and low-dense portions (no referential numbers) stretched a large amount are alternately provided in the width direction W of the side flap portions 10. Each front-side stretched region 15 is stretched by a factor of 1.5 to 3.0 compared to the original length thereof before stretching. If the stretching ratio of each front-side stretched region 15 is less than 1.5, the height of the standing side flap portion 10 is so small that the elastic members 12a to 12c could not come into close contact with the skin. On the other hand, if the stretching ratio of each front-side stretched region 15 exceeds 3.0, a lot of damage due to stretching could cause material defects such as tears and holes. By setting the stretching ratio of each front-side stretched region 15 in a range of 1.5 to 3.0, a space between the absorbent body 2 and skin, or a so-called pocket, can be formed without a fear of causing material defects. [0035] Each front-side stretched region 15 has such a transparency that excretion inside is visible from the outside when the diaper is wom. In the other words, the transmittance of the front-side stretched region 15 is a transmittance from the outside to the inside. The light transmittance thereof is increased by not less than 3% by the stretching process. If the light transmittance is not less than 61% (measured by JIS K7105), excretion inside is visible from the outside. [0036] Moreover, each front-side stretched region 15 of this embodiment is provided across the entire region between the absorbent body 2 and the elastic member 12a, which is located at the outermost position, in the width direction W of the side flap portion 10. Each front-side stretched region 15 is provided across the entire range of the front-side region S3 in the longitudinal direction L of the side flap portion 10 so as to reach the end of the front-side region S3. In this embodiment, each front-side stretched region 15 is not extended to the crotch or back-side regions S2 and S1. The specific method of forming the front-side stretched regions 15 is described in detail below. [0037] The waist flap portion part is composed of a pair of back waist flap portions 20 and a pair of front waist flap portions 21. One end of each of the pair of back waist flap portions 20 is fixed to one of the pair of side flap portions 10 in the back-side region S1. A locking portion 22 is provided at a top end of each back waist flap portion 20. 8 G2080100(JUN-048-PCT)_Eng. Spec_Final.doc [0038] Each locking portion 22 is a hook-and-loop fastener for locking with mechanical locking force or adhesive tape for locking with adhesive force. When the locking portion 22 is a hook-and-loop fastener, the material of each front waist flap portion 21 is composed of a sheet material having nonwoven fabric at least in the surface. [0039] Next, the method of forming the front-side stretched region 15 is briefly described using Fig. 8. Fig. 8 is a cross-sectional view of a stretching apparatus. [0040] Each side flap portion 10 is formed by bonding the backsheet 4 and exterior sheet 11 to each other with a heat-sensitive adhesive (a hot-melt adhesive or the like, for example. Hereinafter, referred to as HMA) applied using spiral spray in a diameter of 15 mm and a basis weight of 5 g/m 2 . [0041] The backsheet 4 is made of non-breathable film with a basis weight of 23.5 g/m 2 . The exterior sheet 11 is made of SMS with a basis weight of 13 g/m 2 . [0042] As shown in Fig. 8, a stretching apparatus 30 forming the front-side stretched regions 15 includes a pair of stretching blade units 31 which face each other and can be meshed with each other. Each of the stretching blade units 31 is configured to have a 2.5 mm blade depth, a 1.25 mm pitch between a pair of blades, and 17 blades. The stretching apparatus 30 performs the stretching processing with a temperature of the stretching blade units 31 set to 1000C. With such a stretching process, the front-side stretched regions 15 are 1.8 times longer than before stretching. [0043] Stretching with the stretching apparatus 30 alternately provides the dense portions stretched a small amount and the low-dense portions stretched a large amount in the width direction (the waistline direction) of the side flap portions 10 in the front-side stretched regions 15. [0044] As for the width of the front-side stretched regions 15 subjected to the stretching process, it is preferable that width W1 (Figs. 4 and 7) ranges from 1. 5 to 3.0 times width W2 (Figs. 6 and 7) in the case where the elastic members are provided in the side flap portions 10. [0045] The width W1 refers to a distance from the side edge of the absorbent body 2 to the vicinity of the inside of the elastic member 12c, which is located closest to the absorbent body 2 among the outer three elastic members 12a to 12c provided in each side flap portion 10, in a place where the side flap portion 10 has the smallest width when expanding in the width direction W. In other words, the width W1 is a referential width of each side flap portion 10 before the stretching process. 9 G2080I00(JUN-048-PCT)_ Eng. SpecFinal.doc [0046] The width W2 refers to a distance from the side edge of the absorbent body 2 to the vicinity of the inside of the elastic member 12c in a place where the side flap portion 10 has the largest width when expanding in the width direction W. [0047] When the elastic member 12c is not provided in the widest part of each side flap portion 10 unlike the embodiment, the width W2 is calculated assuming an extension of the elastic member 12c extending in the longitudinal direction L. In other words, the width W2 is referential width of each side flap portion 10 after the stretching processing. [0048] When the width W2 is less than 1.5 times the width W1, the short elongation of each front-side stretched region 15 reduced in weight by the stretching processing leads to short distance from the side portions of the absorbent body 2 to the part of the side flap portion 10 where the elastic members are provided. Accordingly, space for accommodating urine leaking from the absorber 5 is small. Excretion can therefore leak from the diaper 1A across the part of each side flap portion 10 where the elastic members are disposed. [0049] When the width W2 is more than 3.0 times the width W1, because of the long elongation of each front-side stretched region 15 reduced in weight by the stretching process, the material is therefore more likely to be damaged due to stretching. Accordingly, the material defects including tears and holes are highly likely to occur. If the material is broken, urine leaks through the broken part. [0050] In the case where the elastic members 12a to 12d are not disposed in each side flap portions 10, similarly to the above description, as for the width between the side edge of the absorbent body 2 and the outer edge of each side flap portion 10 when the side flap portion 10 is expanded in the width direction W, it is preferable that the largest width is 1.5 to 3.0 times the smallest width because of the same reason as the above description. [0051] When the wearer wears the diaper 1 A having the aforementioned configuration, the outer edges of the side flap portions 10 snugly fits to the wearer's legs due to the contraction of the elastic members 12a to 12d. In addition, as shown in Fig. 7, the front-side region S3 where the front-side stretched regions 15 are formed expands in the width direction W by a length of the part stretched by the stretching processing and reduced in weight when the diaper 1A is worn. [0052] On the other hand, since the back-side region S1 is not subjected to the stretching process, the back-side region S1 does not expand more than the original width even if the back-side region S1 is tried to be expanded in the width direction W when the diaper 1A is wom. 10 G20801OO(JUN-048-PCT)_Eng. Spec Final.doc [00531 Accordingly, the diaper 1A is put on the body with the front-side region S3 being wider than the back-side region S1 when the diaper 1A is wom. When the wearer wears the diaper 1A, as for the distance between the elastic members 12a and 12d as well, the diaper 1A is put on the body with the distance between the elastic members 12a and 12d being longer on the front side Fr than that on the back side Ba. [0054] The diaper 1A can be fit along the wear's groin part when the wearer wears the diaper 1A. The diaper 1A is thus excellent in wearability. [0055] In the diaper 1 A, a space, or a so-called pocket is formed in an area surrounded by the wearer, the absorbent body 2, and the pair of side flap portions 10 on the front side Fr. The diaper IA can temporarily hold urine in the pocket and can prevent leakage of urine as much as possible. [0056] The front-side stretched regions 15 are formed by partially stretching the pair of side flap portions 10. In the manufacturing process of the diaper 1A, therefore, it is unnecessary to make each side flap portion 10 larger in the width direction W on the front side Fr than the other part. The side edges of the diaper 1A on the front side Fr do not need to be curved in the manufacturing process. [0057] As described above, in the diaper 1 A which is capable of fitting to a wearer and forms a space between the wearer and the absorbent body 2 on the front side Fr, the diaper 1A is made of less materials and manufactured with simpler processing at lower cost accordingly. [0058] In addition, the diaper 1A can be manufactured with the elastic members 12a to 12c being disposed in each side flap portion 10 longitudinally in a liner fashion, and the processing process of the diaper 1A can be therefore facilitated. Moreover, the front-side stretched regions 15 of the side flap portions 10 are formed by stretching the side flap portions 10 in the width direction W with the stretching processing. Accordingly, each side flap portion 10 before the stretching processing can be made of a substantially straight material. In the manufacturing process of the diaper 1A, it is therefore possible to cut the waste of the materials due to cut out and facilitate the processing. [0059] Moreover, part of each side flap portion 10 covering the wearer's leg near his/her crotch is the front-side stretched region 15, which is thin and soft. Accordingly, the diaper 1A can reduce uncomfortable feeling. Furthermore, the diaper 1A can be improved in capability of following the movement of wearer's hips. Still furthermore, the front-side stretched regions 15 have an advantage of easily standing perpendicular to the absorbent body 2. [0060] 11 G2080100(JUN-048-PCT)_Eng. Spec Final.doc The front-side stretched regions 15 reach the end of the diaper 1 A on the front side Fr in this embodiment but may be provided so as not to reach the end of the diaper IA on the front side Fr. However, it is more preferable that the front-side stretched regions 15 are provided to reach the end of the diaper 1A on the front side Fr like this embodiment in the light of a better fit to the wearer. [0061] In this embodiment, each front-side stretched region 15 is provided between the absorbent body 2 and the elastic member 12a, which is located at the outermost position. Specifically, each front-side stretched region 15 is provided in a half on the absorbent body 2 side of the central line dividing in halves in the width direction W a region between the side edge of the absorbent body 2 and the elastic member 12a, which is located at the outermost position. Accordingly, the diaper 1A has the following advantages, too. Even in the diaper 1A including the elastic members 12a to 12d provided in the pair of side flap portions 10, the elastic members 12a to 12d only need to be provided in each side flap portion 10 in a linear fashion. It is therefore possible to facilitate the processing of the elastic member-attached diaper and reduce the cost accordingly. When the wearer wears the diaper 1A, the diaper 1A bends at the places where the rigidity changes, or at the boundaries between the absorbent body 2 and the side flap portions 10. In this embodiment, the boundaries between the absorbent body 2 and the side flap portions 10 are positioned at the flexible front-side stretched regions 15, thus providing good standing properties. [0062] In this embodiment, since each front-side stretched region 15 has such a transparency that excretion inside is visible from the outside when the diaper 1A is wom, the presence of excretion within the diaper 1A can be checked through the front-side stretched region 15. It is therefore possible to easily determine the time for replacement of the diaper 1A and the like. [0063] In this embodiment, each front-side stretched region 15 includes the dense portions stretched a small amount and low-dense portions stretched a large amount alternately provided in the width direction W of the side flap portion 10. Accordingly, each front-side stretched region 15 is alternately folded in opposite directions due to the dense and low-dense portions in the manufacturing process of the diaper 1A. The outer edge of each side flap portion 10 therefore forms a straight line without protruding. Accordingly, the diaper 1A can be improved in handling at the manufacturing process, product packaging process, and the like. [0064] (Embodiment 1-2) Fig. 9 is a plan view of a diaper 1 B according to Embodiment 1-2 of the present invention, showing the diaper 1 B with the width expanded to be wom. [0065] In this embodiment, the front-side stretched regions 15 expanded (when the diaper 1 B is wom) have varying width not constant width. 12 G20801OO(JUN-048-PCT)_Eng. Spec_Final.doc [0066] As shown in Fig. 9, the diaper 1 B according to Embodiment 1-2 differs from Embodiment 1-1 in terms of the stretching ratio of the front-side stretched regions 15. Specifically, when the diaper 1B is expanded in the width direction W (when the diaper 1 B is worn), a width dimension Li of each front-side stretched region 15 in a crotch-section side part T2 is larger than a width dimension L2 thereof in an end-side part on the front side Fr. [0067] Such width dimension can be implemented by varying the width of a region subjected to the stretching processing between the crotch-section-side part T2 and the end-side-part T1 on the front side Fr or by varying the stretching degree per unit length. [0068] The other configuration is the same as that of the above embodiment. The same components are given the same referential numerals, and the description thereof is omitted. [0069] According to this embodiment, the diaper 1 B in use forms a large space, or a so-called pocket between the diaper 1B and the wearer's skin on the front side Fr. Accordingly, the diaper 1B can temporarily hold a large amount of urine in the large space. The diaper 1B can therefore more surely prevent leakage of excretion. [0070] (Embodiment 1-3) Fig. 10 is a cross-sectional view of a diaper 1C according to Embodiment 1-3 of the present invention. [0071] As shown in Fig. 10, the diaper 1C according to Embodiment 1-3 differs from Embodiment 1-1 in terms of the configuration of the absorbent body 2 and the configuration of the front-side stretched region 15 of each side flap portion 10. Specifically, the topsheet 3 and backsheet 4 in the absorbent body 2 are joined by a joint portion 6 only at central portion of the diaper 1C in the width direction W and are not joined at both ends of the diaper 1C in the width direction W. Each front-side stretched region 15 is extended so as to overlap the absorbent body 2 (to a region where the topsheet 3 and backsheet 4 are not joined to each other) in a plan view of the diaper 1C. [0072] The other configuration is the same as that of Embodiment 1-1. The redundant description is omitted, and the same components in the drawing are given the same reference numerals for clarification. [0073] In this embodiment, front-side stretched regions 15 are extended so as to overlap the absorbent body 2, so that each front-side stretched region 15 has a large width dimension. In the diaper 1C, 13 G20801OO(JUN-048-PCT)_Eng. SpecFinal.doc therefore, the depth of the space, a so-called pocket, formed on the front side Fr of the diaper 1C, can be made deep. [0074] (Embodiment 1-4) Fig. 11 is a cross-sectional view of a diaper 1 D according to Embodiment 1-4 of the present invention. [0075] As shown in Fig. 11, the diaper 1D according to Embodiment 1-4 differs from Embodiment 1-1 in terms of only the configuration of each side flap portion 10. Each side flap portion 10 is divided into an inner flap portion 10a and an outer flap portion 1 Oa in the outside of the side flap portion 10 in the width direction W. The inner flap portion 10a is made of a sheet material of good texture. At the end of the inner flap portion 10a, the stretched elastic member 12e is provided. At the end of the outer flap portion 10a, the stretched elastic members 12a to 12c are provided. Each side flap portion 10 doubly snugly fit to the leg, and the diaper 1 D can surely prevent side leakage. The diaper 1 D feels nice and soft since the inner flap portions 1 a are made of a sheet material of good texture. [0076] The other configuration is the same as that of Embodiment 1-1. The redundant description is omitted, and the same components in the drawing are given the same reference numerals for clarification. [0077] In Embodiment 1-4, the elastic members 12a to 12c and 12e are provided at the ends of the inner and outer flap portions 10a and 10b. However, in a diaper according to a modification of Embodiment 1-4, the expanded elastic members may be provided only at the end of the inner flap portion I0a. The diaper according to the modification of Embodiment 1-4 has a so-called inwardly inclining three-dimensional gather structure. [0078] Figs. 12 to 16 show a diaper 1E according to Embodiment 1-5 of the present invention. Fig. 12 shows a plan view of a developed state of the diaper 1 E. Fig. 13 shows a cross-sectional view of Fig. 12 taken along a line C-C. Fig. 14 is a cross-sectional view of Fig. 12 taken along a line D-D. Fig. 15 shows a cross-sectional view of the diaper in use. Fig. 16 is a developed plan view showing the diaper in use. [0079] In the aforementioned embodiments, the front-side stretched regions 15 are provided in the side flap portions in the front-side region S3. In Embodiments 1-5 to 1-9 described below, back-side stretched regions 14 are provided in the side flap portions in the back-side region S1. [0080] The other configuration is the same as that of the aforementioned embodiments, and the same 14 G20801OO(JUN-048-PCT)_Eng. Spec_Final.doc portions are given the same number, and the description thereof is omitted. [0081] As shown in Figs. 12 to 14, in each side flap portion 10, the back-side stretched region 14 stretched in the waistline direction (the width direction W) is provided between the absorbent body 2 and the elastic member 12a located at the outermost position in the back-side region S1. Specifically, each back-side stretched region 14 is provided between the side edge of the absorbent body 2 and the vicinity of the inside of the elastic member 12c, which is located closest to the absorbent body 2 among the outer three elastic members 12a to 12c provided in the side flap portion 10. Each back-side stretched region 14 is a region stretched by the stretching processing in the width direction W, which is orthogonal to the longitudinal direction L from the back side Ba to the front side Fr so as to have a lower weight than the other region. In the back-side stretched region 14, dense portions (with no referential numbers) stretched a small amount and low-dense portions (with no referential numbers) stretched a large amount are alternately provided in the width direction W of the side flap portions 10. Each back-side stretched region 14 is stretched by a factor of 1.5 to 3.0 compared to the original width before stretching. If the stretching ratio of each back-side stretched region 14 is less than 1.5 times, the height of the standing side flap portion 10 is so small that the elastic members 12a to 12c could not come into close contact with the skin. On the other hand, if the stretching ratio of each back-side stretched region 14 exceeds 3.0 times, a lot of damage due to stretching could cause material defects such as tears and holes. By setting the stretching ratio of each rear-side stretched region 14 in a range of 1.5 to 3.0, a space or a so-called pocket can be formed in the diaper 1 E without a fear of causing material defects. [0082] Each back-side stretched region 14 has such a transparency that excretion inside is visible from the outside when the diaper is wom. The transmittance of each back-side stretched region 14 is a transmittance from the outside to the inside. [0083] Moreover, each back-side stretched region 14 if this embodiment is provided across the entire region between the absorbent body 2 and the elastic member 12a, which is located at the outermost position, in the width direction W of the side flap portion 10. Each back-side stretched region 14 is provided across the entire range of the back-side region S1 in the longitudinal direction L of the side flap portion 10 so asto reach the end of the back-side region S1. In this embodiment, each back-side stretched region 14 is not extended to the crotch or front-side regions S2 and S3. The specific method of forming the back-side stretched regions 14 is the same as that of the front stretched region 15 of the aforementioned embodiments, and the description thereof is omitted. [0084] As for the width of the back-side stretched regions 14 subjected to the stretching process, it is preferable that width W4 (Figs. 15 and 16) ranges from 1. 5 to 3.0 times width W3 (Figs. 13 and 16) in the case where the elastic members are provided in the side flap portions 10. [0085] 15 G20801OO(JUN-048-PCT)_Eng. Spec_Final.doc The width W3 refers to a distance from the side edge of the absorbent body 2 to the vicinity of the inside of the elastic member 12c, which is located closest to the absorbent body 2 among the outer three elastic members 12a to 12c provided in each side flap portion 10, in a place where the side flap portion 10 has the smallest width when the diaper 1E is expanded in the width direction W. In other words, the width W3 is a referential width of each side flap portion 10 before the stretching process. [0086] The width W4 refers to a distance from the side edge of the absorbent body 2 to the vicinity of the inside of the elastic member 12c in a place where the side flap portion 10 has the largest width when the diaper 1 E is expanded in the width direction W. [0087] In the case where the elastic members 12c are not provided in the widest part of each side flap portions 10 unlike the embodiment, the width W4 is calculated assuming an extension of the elastic member 12c extending in the longitudinal direction L. In other words, the width W4 is referential width of each side flap portion 10 after the stretching processing. [0088] When the width W4 is less than 1.5 times the width W3, the short elongation of each back-side stretched region 14 reduced in weight by the stretching processing leads to short distances from the side portions of the absorbent body 2 to the part of the side flap portion 10 where the elastic members are provided. Accordingly, space for accommodating excretion leaking from the absorber 5 is small. Excretion could therefore leak from the diaper 1 E across the part of each side flap portion 10 where the elastic members are disposed. [0089] When the width W4 is more than 3.0 times the width W3, because of the long elongation of each back-side stretched region 14 reduced in weight by the stretching process, the material is therefore more likely to be damaged due to stretching. Accordingly, the material defects including tears and holes are highly likely to occur. If the material is broken, the broken part can leak excretion. [0090] In the case where the elastic members 12a to 12d are not disposed in the side flap portions 10, similarly to the above description, as for the width between the side edge of the absorbent body 2 and the outer edge of each side flap portion 10 when the side flap portion 10 is expanded in the width direction W, it is preferable that the largest width is 1.5 to 3.0 times the smallest width because of the same reason as the above description. [0091] Such a relationship allows a large pace to be formed between the wearer and the absorbent body 2 with the wearer's hips folded with the absorbent body 2 and portions of the pair of side flap portions 10 on the back side Ba. Accordingly, the diaper 1E can temporarily hold a large amount of discharged excretion in the large space. The diaper 1 E can more surely prevent leak of excretion. 16 G2080100(JUN-048-PCT)_Eng. Spec_Final.doc [0092] Preferably, the material of the exterior sheet suitable for the stretching processing has a film fracture elongation of 750% or more. Materials with a film fracture elongation of less than 750% are subject to pin holes at the stretching process. The pin holes are highly likely to cause leakage of excretion. [0093] The transmittance of the back-side stretched region 14 varies on the type of the sheet material of the side flap portions 10. Accordingly, the transmittance from the inside to the outside is obtained by adjusting the elongation depending on the type of the sheet material. [0094] When the wearer wears the diaper 1 E having the aforementioned configuration, the outer circumference of each side flap portion 10 snugly fits around the wearer's leg due to the contraction of the elastic members 12a to 12d. In addition, as shown in Fig. 16, when the diaper 1E is wom, the back-side region S1 where the back-side stretched regions 14 are formed expands in the width direction W by a length of the portion stretched by the stretching processing and reduced in weight. [0095] On the other hand, since the front-side region S3 is not subjected to the stretching process, the front-side region S3 does not expand more than the original width even if the front-side region S3 is tried to be expanded in the width direction W when the diaper 1 E is wom. [0096] Accordingly, the diaper 1 E is put on the body with the back-side region S1 being wider than the front-side region S3 when the diaper 1E is wom. As for the distance between the elastic members 12a and 12d as well, when the wearer wears the diaper 1 E, the diaper 1 E is put on the body with the distance between the elastic members 12a and 12d being longer on the back side Ba than that on the front side Fr. [0097] The diaper 1 E can be therefore fit to wrap around the wearer's hips on the back side Ba. The diaper 1 E is thus excellent in wearability. [0098] The diaper 1 E forms a spatial margin between the wearer and the diaper 1 E while wrapping around the wearer's hips. The diaper 1E can temporarily hold even loose feces excreted. The diaper 1E can therefore prevent loose faces escaping from the absorber from leaking across the elastic members 12a to 12d around the legs. [0099] The back-side stretched regions 14 are formed by the stretching processing stretching in the width direction W. Accordingly, each side flap portion 10 before the stretching processing can be made of a substantially straight material. In the manufacturing process of the diaper 1 E, it is therefore possible to cut the waste of materials due to cut out and facilitate the processing. 17 G20801OO(JUN-048-PCT)_Eng. Spec_Final.doc [0100] Moreover, part of each side flap portion 10 covering the wearer's leg near his/her crotch is the back-side stretched region 14, which is thin and soft. Accordingly, the diaper 1 E can reduce uncomfortable feeling. Furthermore, the diaper 1 E can be improved in capability of following the movement of wearer's hips. Still furthermore, the back-side stretched regions 14 have advantages of easily standing perpendicular to the absorbent body 2 and allowing the diaper 1 E to fit to the hips without excessively tightening the outer edge of each side flap portion 10 and the like. [0101] The back-side stretched regions 14 reach the end of the diaper 1E on the back side Ba in this embodiment but may be provided so as not to reach the end of the diaper 1 E on the back side Ba. However, it is more preferable that the back-side stretched regions 14 are provided to reach the end of the diaper 1 E on the back side Ba like this embodiment in the light of a fit to the wearer. [0102] In this embodiment, each back-side stretched region 14 is provided between the absorbent body 2 and the elastic member 12a, which is located at the outermost position. Specifically, each back-side stretched region 14 is provided in a half on the absorbent body 2 side of the central line dividing in halves in the width direction W a region between the side edge of the absorbent body 2 and the elastic member 12a, which is located at the outermost position. Accordingly, the diaper 1 E has the following advantages, too. Even in the diaper 1E including the elastic members 12a to 12c provided in the pair of side flap portions 10, the elastic members 12a to 12c only need to be provided in each side flap portion 10 in a linear fashion. It is therefore possible to facilitate the processing of the elastic member-attached diaper and reduce the cost accordingly. When the wearer wears the diaper 1 E, the diaper 1 E bends at the positions where the rigidity changes, or at the boundaries between the absorbent body 2 and the side flap portions 10. In this embodiment, the boundaries between the absorbent body 2 and the side flap portions 10 are positioned at the flexible back-side stretched regions 14, thus providing good standing properties and improving the fit to the hips. [0103] In this embodiment, since each back-side stretched region 14 has such a transparency that excretion inside is visible from the outside when the diaper 1 E is worn, the presence of excretion within the diaper 1 E can be checked through the back-side stretched region 14. It is therefore possible to easily determine the time for replacement of the diaper 1 E and the like. [0104] In this embodiment, each back-side stretched region 14 includes the dense portions stretched a small amount and low-dense portions stretched a large amount alternately provided in the width direction W of the side flap portion 10. Accordingly, each back-side stretched region 14 is alternately folded in opposite directions due to the dense and low-dense portions in the manufacturing process of the diaper 1E. The outer edge of each side flap portion 10 therefore forms a straight line without protruding. Accordingly, the diaper 1 E can be improved in handling at the manufacturing process, product packaging process, and the like. 18 G20801OO(JUN-048-PCT)_Eng. SpecFinal.doc [0105] (Embodiment 1-6) Fig. 17 is a plan view of a diaper 1 F according to Embodiment 1-6 of the present invention, showing the diaper 1 B with the width expanded for use. [0106] As shown in Fig. 17, the diaper 1 F according to Embodiment 1-6 differs from Embodiment 1-5 in terms of the stretch ratio of the back-side stretched regions 14. Specifically, when the diaper 1 F is expanded in the width direction W (when the diaper 1 F is wom), a width dimension L3 of each back-side stretched region 14 in a crotch-section side part T4 is larger than a width dimension L4 thereof in an end part on the back side Ba. [0107] The other configuration is the same as that of Embodiment 1-5. The same components are given the same referential numerals, and the description thereof is omitted. [0108] According to this embodiment, the diaper 1 F in use forms a large space between the wearer's hips and the absorbent body 2. Accordingly, the diaper 1 F can temporarily hold a large amount of excretion. The diaper 1 F can therefore more surely prevent excretion from leaking. [0109] (Embodiment 1-7) Fig. 18 is a plan view of a developed state of a diaper 1 G according to Embodiment 1-7 of the present invention. [0110] In this embodiment, in the pair of side flap portions 10, the back-side stretched regions 14 are formed in the back-side region S1 while the front-side stretched regions 15 are formed in the front-side region S3. Accordingly, the diaper 1G is wider in the back and front-side regions S1 and S3 than in the crotch region S2 and can form spaces on both the back and front sides Ba and Fr. The diaper 1G therefore forms a space between the wearer and the absorbent body 2 with the wearer's crotch portion wrapped around by the absorbent body 2 and the pair of side flap portions 10 also on the front side Fr. The diaper 1G can temporarily hold a large amount of excretion in the both spaces on the back and front sides Ba and Fr, thus preventing leakage of excretion as much as possible. [0111] Also in the front-side stretched regions 15, similarly to Embodiment 1-6, the stretching ratio can be made different between the crotch- and back-side regions. This can provide a diaper excellent in wearability. [0112] (Embodiment 1-8) 19 G20801OO(JUN-048-PCT)_Eng. SpecFinal.doc Fig. 19 is a cross-sectional view of a diaper 1 H according to Embodiment 1-8 of the present invention. [0113] As shown in Fig. 19, the diaper 1 H according to Embodiment 1-8 differs from Embodiment 1-5 in terms of the configuration of the absorbent body 2 and the configuration of the back-side stretched region 14 of each side flap portion 10. Specifically, the topsheet 3 and backsheet 4 in the absorbent body 2 are joined by the joint portion 6 only at central part in the width direction W and are not joined at both ends in the width direction W. Each back-side stretched region 14 is extended so as to overlap the absorbent body 2 (to a region where the topsheet 3 and backsheet 4 are not joined to each other) in a plan view of the diaper 1 H. [0114] The other configuration is the same as that of Embodiment 1-5. The redundant description is omitted, and the same components in the drawing are given the same reference numerals for clarification. [0115] In this embodiment, the back-side stretched regions 14 are extended so as to overlap the absorbent body 2, so that each back-side stretched region 14 has a large width dimension. The diaper 1H can therefore have large part for wrapping the wearer's hips and large space or so-called pocket formed on the back side Ba of the diaper 1 H. [0116] (Embodiment 1-9) Fig. 20 is a cross-sectional view of a diaper 11 according to Embodiment 1-9 of the present invention. [0117] As shown in Fig. 20, the diaper 11 according to Embodiment 1-9 differs from Embodiment 1-5 in terms of only the configuration of each side flap portion 10. Each side flap portion 10 is divided into the inner flap portion 1 0a and the outer flap portion 1 0a in the outside of the side flap portion 10 in the width direction W. The inner flap portion 10a is made of a sheet material of good texture. At the end of the inner flap portion 10a, the extended elastic member 12e is provided. At the end of the outer flap portion 10a, the extended elastic members 12a to 12c are provided. Each side flap portion 10 doubly fit snugly to the legs, and the diaper 11 can more surely prevent side leakage. The diaper 11 feels nice and soft since the inner flap portions 1 0a are made of a sheet material of good texture. The other configuration is the same as that of Embodiment 1-5. The redundant description is omitted, and the same components in the drawing are given the same reference numerals for clarification. [0118] (Modifications of above Embodiments) In a diaper according to a modification of each of the aforementioned embodiments, in the crotch region S2, crotch-side stretched regions can be provided between the absorbent body 2 and the 20 G20801OO(JUN-048-PCT)_Eng. Spec_Final.doc elastic members 12a located at the outermost position in the side flap portions 10. [0119] The crotch-side stretched regions can be formed by stretching each side flap portion 10 in the crotch region S2 in the width direction W. In the diaper according to the modification, provision of the crotch-side stretched regions in such a manner allows the outer edge of each side flap portion 10 to come into close contact with the wearer's legs due to construction of each elastic member. [0120] Moreover, each side flap portion 10 has an expandable width dimension larger in the crotch region S2 than those in the crotch and front-side regions S2 and S3 because of the crotch-side stretched region. Accordingly, space, a so-called pocket is formed under the wearer's crotch. In the diaper according to the modification, the pocket can be formed under the crotch without providing a tum-back in each side flap portion 10, providing a curved edge in each side flap portion 10, or providing the elastic members in a curved fashion along the curved edge of each side flap portion 10 in the width direction W. Accordingly, the manufacturing process of the diaper according to the modification makes it possible to reduce the materials for use, facilitates the processing, and reduce the cost accordingly. [0121] In the present invention, the front- and back-side stretched regions 15 and 14 are formed for the backsheet 4 and exterior sheet 11. However, the front- and back-side stretched regions 15 and 14 may be formed by performing the stretching processing for only the backsheet 4. In this case, the amount of used nonwoven fabric can be reduced. [0122] The front and back-side stretched regions 15 and 14 may be formed by stretching bonded part of the three materials of the topsheet 3, backsheet 4, and exterior sheet 11. In this case, body fluid escaping from the absorber 5 can be again introduced to the absorber 5 with the hydrophilic topsheet 3. [0123] In the present invention, a liquid-impermeable sheet of a different material from the backsheet 4 may be layered on the exterior sheet 11 in each of the pair of side flap portions 10. The front and back-side stretched regions 15 and 14 are formed by stretching the layered portion of the exterior sheet 11 and the liquid-impermeable sheet. In this case, the liquid-impermeable sheet is a sheet material suitable for the stretching processing while part of the backsheet 4 under the absorber 5 can be made of breathable film, high basis weight film for preventing pin holes, or the like. It is thus possible to employ material suitable for each portion. [0124] In each embodiment, the four elastic members 12a to 12d are provided in each side flap portion 10. However, the number and positions of the elastic members can be properly changed, and it is possible to provide one or two elastic members in a side edge of each side flap portion 10. 21 G20801OO(JUN-048-PCT)_Eng. Spec_Final.doc [0125] Each embodiment shows the case where the present invention is applied to an open-type diaper, but the present invention can be applied to a pant-type diaper in a similar manner. The present invention can be also applied to absorbent articles besides the diapers. [0126] The entire contents of Japanese Patent Application No. 2008-037919 filed on February 19, 2008, Japanese Patent Application No. 2009-026246 filed on February 6, 2009, and Japanese Patent Application No. 2009-026255 filed on February 6, 2009 are incorporated herein by reference. [0127] (Embodiment 2-1) [Background Art] Absorbent articles each including a liquid-permeable topsheet, a liquid-impermeable backsheet, and an absorber absorbing and retaining liquid have been widely known. The absorber is disposed between the liquid-permeable topsheet and the liquid-impermeable backsheet. Regarding such absorbent articles, Patent Literature 1 discloses a structure in which the topsheet is made of liquid-impermeable nonwoven fabric and a meltblown layer is provided between the absorber and backsheet. [0128] Patent Literature 2 discloses a structure in which a folded portion is formed in the liquid-impermeable backsheet and is bonded to liquid-impermeable fabric. The folded portion is formed along both side edges of the absorber extending toward the topsheet side. [0129] Patent Literature 3 discloses a structure in which side flap portions extending from both lateral side edges of an absorber outward in the lateral direction is composed of a composite sheet which is different from the topsheet or backsheet. The composite sheet is formed of an inner layer composed of a water impermeable sheet with a thickness of 5 pm or more and less than 20 pm and an outer layer composed of nonwoven fabric with a basis weight of 10 to 25 g/m2, which abut on each other. [0130] (Patent Literature 1) Japanese Patent Laid-open Publication No. 2001-104372 (Patent Literature 2) Japanese Patent Laid-open Publication No. 2005-211131 (Patent Literature 3) Japanese Utility Model Laid-open Publication No. 7-21020 [Disclosure of the Invention] However, in the absorbent article described in Patent Literature 1, the topsheet made of nonwoven fabric has a limited leakage preventing function. If body fluid blocked by the topsheet is subjected to excessive pressure accompanied with active movement of the wearer, the body fluid penetrates the topsheet, causing side leak from the topsheet. The topsheet made of nonwoven fabric has a problem of exuding and leaking particularly a fluid with high viscosity and low surface tension such as 22 G20801OO(JUN-048-PCT)_Eng. SpecFinal.doc loose faces. [0131] In the absorbent article described in Patent Literature 2, if the backsheet is made of film having the same physical properties as those of the lower surface of the absorber, the increased water pressure resistance can prevent the leakage of excretion. However, in the lower surface of the absorber subjected to body pressure, pinholes are highly likely to occur and leak excretion. Accordingly, part of the film in the lower surface of the absorber is made thick. However, the other part not subjected to body pressure is unnecessarily made thick. The lower surface of the absorber is therefore hard and has bad texture. Moreover, the lower surface of the absorber has poor breathability, and the diaper feels moist. [0132] In the absorbent article described in Patent Literature 3, since the absorber and the side flap portion in the side part are bonded to each other, the materials thereof are overlapped on each other and are redundant. Moreover, it is necessary to employ different materials for the absorber and the side part, leading to an increased number of materials. The equipment for manufacturing the absorbent article is therefore complicated. Moreover the absorber and the side flap portion are joined by bonding and could be separated. If the joined part is separated, the absorbent article could leak excretion. [0133] As described above, any of the conventional arts cannot provide an absorbent article capable of being prevented from leaking and exuding and feeling less damp. [0134] An object of the present invention is to provide a well-breathable absorbent article prevented from exuding and leaking. [0135] An aspect of the present invention is an absorbent article (for example, a diaper 1 001A) including: an absorbent body (an absorbent body 1002) which is composed of a liquid-permeable topsheet (a topsheet 1003), a liquid-impermeable backsheet (a backsheet 1004), and an absorber (an absorber 1005) disposed between the topsheet and the backsheet and configured to absorb and retain liquid, the absorbent body having a back-side region (back-side region S11), a crotch region (a crotch region S12), and a front-side region (a front-side region S13) located in a longitudinal direction (a longitudinal direction L) from the back side to the front side when the absorbent article is wom; and a pair of right and left side flap portions (side flap portions 1010) provided on both sides of the absorbent body in the width direction (a width direction W). In the absorbent article, portions of the backsheet located in a lower surface of the absorbent body and in the side flap portions are composed of a continuous single component, and each side flap portion includes a highly moisture-permeable region (a highly moisture-permeable region 1006) having higher moisture permeability than that of the lower surface of the absorbent body. 23 G20801OO(JUN-048-PCT)_Eng. SpecFinal.doc [0136] According to the present invention, since the lower surface of the absorbent body and the portions of the backsheet of the side flap portions are monolithically formed, the absorbent article can be prevented from exuding and leaking. Moreover, each side flap portion serves as a highly moisture permeable region. Accordingly, the absorbent article has high breathability and high moisture permeability and is therefore prevented from feeling damp. According to the present invention, it is possible to provide a well-breathable absorbent article prevented from exuding and leaking. [0137] [Modes for Carrying out the Invention] Fig. 21 is a cross-sectional view of the diaper 1001A of Embodiment 2-1 of the present invention. The diaper 1001 A as an absorbent article includes an absorbent body 1002 and the pair of right and left side flap portions 1010 provided on both sides of the absorbent body 1002 in the width direction W. The width direction W of the absorbent body 1002 refers to a direction orthogonal to the longitudinal direction L from the back side to the front side in a plan view of the diaper 1001A. [0138] The absorbent body 1002 includes at least the liquid-permeable topsheet 1003, the liquid-impermeable backsheet 1004, and the absorber 1005 disposed between the topsheet 1003 and the backsheet 1004 and configured to absorb and retain liquid. The both edges of the topsheet 1003 in the width direction W are folded so as to wrap around the absorber 1005. The folded portions of the topsheet 1003 and the absorber 1005 are bonded to the backsheet 1004 with glue such as a hot melt adhesive. [0139] The topsheet 1003 is made of hydrophilic nonwoven fabric, woven fabric, perforated plastic film, or perforated hydrophobic nonwoven fabric. In this embodiment, the topsheet 1003 is made of SMS with a basis weight of 10 g/m 2 (composite nonwoven fabric of spunbond and meltblown fabric, and hereinafter referred to as SMS). [0140] The absorber 1005 is a laminate including liquid absorption and retention characteristics. Specifically, the absorber 1005 is composed of a mixture of absorbent pulp and a highly absorbent polymer. [0141] The backsheet 1004 is composed of microporous liquid-impermeable film made of resin containing an inorganic material as a filler. Specifically, the liquid-impermeable film is a microporous moisture permeable sheet which is made of polyethylene with a basis weight of 22.0 g/m 2 and contains about 50 wt% calcium carbonate as the filler. The filler can be an inorganic material such as barium sulfate in addition to calcium carbonate. The resin for the moisture permeable sheet can be olefin-based thermosetting resin such as polypropylene, in addition to polyethylene. [0142] 24 G20801OO(JUN-048-PCT)_Eng. SpecFinal.doc The lower surface of the absorbent body 1002 and the portions of the backsheet 1004 located in the side flap portions 101 are composed of a continuous single component. Specifically, the side flap portions 1010 are formed in extensions of the backsheet 1004 on right and left sides from the lower surface of the absorber 1005. The side flap portions 1010 are located on both sides of the absorber 1005. Each side flap portion 1010 includes a highly moisture-permeable region 1006 having higher moisture permeability than that of the lower surface of the absorbent body 1002. In Fig. 21, the highly moisture-permeable regions 1006 are provided on both right and left sides of the absorbent body 1002. The moisture permeability of the highly moisture-permeable regions 1006 is set to 1.3 to 2.5 times or more the moisture permeability of the lower surface of the absorbent body 1002 so that liquid does not escape. Setting the moisture permeability so that liquid does not escape refers to setting the permeability of the highly moisture-permeable regions 1006 in such a range that does not allow leakage of liquid. [0143] The highly moisture-permeable regions 1006 are formed by stretching each side flap portion 1010 composed of a liquid-impermeable sheet in the width direction W (hereinafter, referred to as stretching processing). The stretching processing is described in detail in Embodiment 2-2 described later. [0144] In the outsides of the side flap portions 1010 in the width direction, exterior sheets 1011 composed of liquid-impermeable sheets are provided. In a side edge of each exterior sheet 1011, a gather portion is provided, in which extended elastic members 1012 are disposed along the longitudinal direction L. The gather portions have a higher moisture-permeability than the highly moisture-permeable regions 1006 of the side flap portions 1010. The relationship of the permeability in the diaper 1001A is as follows: the lower surface of the absorbent body 1002 < the highly moisture-permeable regions 1006 < the gather portions. [0145] In Embodiment 2-2, since the backsheet 1004 made of the liquid-impermeable sheet is provided in the lower surface of the absorber 1005, the diaper 1001A can be prevented from exuding and leaking body fluid and the like. [0146] By stretching the side flap portions 1010 in the width direction W, the liquid-impermeable sheet (backsheet 1004) is extended by the width of the stretched part. This results in increased size of the micropores due to the filler, thus leading to higher permeability. The increased permeability provides higher breathability and higher moisture permeability. The diaper 1001A can be therefore prevented from feeling damp inside. Furthermore, the stretching processing softens the materials and improves the wearer's comfort. [0147] (Embodiment 2-2) Figs. 22 to 27 show Embodiment 2-2 of the present invention. Fig. 22 is a plan view of a developed 25 G20801OO(JUN-048-PCT)_Eng. SpecFinal.doc state of a diaper 1001B. Fig. 23 is a cross-sectional view of Fig. 22 taken along a line Al-Al. FIG 24 is a cross-sectional view of Fig. 22 taken along a line B1-B1. Figs. 25 and 26 are plan views of the diaper 1001B illustrating distance for increasing permeability. Fig. 27 is a cross-sectional view of a stretching apparatus. [0148] In Embodiment 2-2 below, the different points from Embodiment 2-1 are mainly described, and the redundant description is omitted. [0149] Similarly to Embodiment 2-1, the diaper 1001 B includes the absorbent body 1002 and the pair of right and left side flap portions 1010 provided on both sides of the absorbent body 1002 in the width direction W. [0150] The absorbent body 1002 includes at least the liquid-permeable topsheet 1003, a liquid-impermeable backsheet 1004, and the absorber 1005 absorbing and retaining liquid. The absorber 1005 is disposed between the topsheet 1003 and the backsheet 1004. The absorbent body 1002 includes the back-side region S11, the crotch region S12, and the front-side region S13 arranged in the longitudinal direction L from the back side to the front side. The absorbent body 1002 covers the back, the crotch and the front sides of the wearer. [0151] The backsheet 1004 is formed by bonding a liquid-impermeable sheet 1013 and the exterior sheet 1011 to each other. The backsheet 1004 composed of the liquid-impermeable sheet 1013 and the exterior sheet 1011 forms the side flap portions 1010. [0152] The extended elastic members 1012 are disposed in the side edge of each side flap portion 1010. In each side flap portion 1010, a part including the exterior sheet 1011 and the liquid-impermeable sheet 1013 laid on each other is subjected to the stretching processing in the width direction W. The part of each side flap portion 1010 subjected to the stretching processing is therefore increased in moisture permeability into the highly moisture-permeable region 1006. [0153] The topsheet 1003 is a liquid-permeable sheet. The topsheet 1003 can be made of hydrophilic nonwoven fabric, woven fabric, perforated plastic film, perforated hydrophobic nonwoven fabric, or the like. In this embodiment, the topsheet 1003 is made of SMS with a weight of 10 g/m 2 . [0154] The liquid-impermeable sheet 1013 of the backsheet 1004 is made of liquid-impermeable microporous film made of resin containing an inorganic material as a filler. [0155] 26 G2080100(JUN-048-PCT)_Eng. Spec_Final.doc Specifically, the liquid-impermeable sheet 1013 can be made of liquid-impermeable film which is moisture permeable or a sheet of such a liquid-impermeable film bonded to nonwoven fabric. In this embodiment, the liquid-impermeable sheet 1013 is composed of a moisture-permeable microporous sheet which is made of polyethylene with a basis weight of 22.0 g/m 2 and contains about 50 wt% calcium carbonate as the filler. The filler can be an inorganic material such as calcium carbonate or barium sulfate. The resin for the liquid-impermeable sheet 1013 can be olefin-based thermosetting resin such as polypropylene in addition to polyethylene. [0156] The exterior sheet 1011 of the backsheet 1004 is a liquid-impermeable sheet. In this embodiment, the exterior sheet 1011 is made of SMS with a basis weight of 13 m/m 2 . The exterior sheet 1011 is disposed from the side of the absorbent body 1002 to the rear surface thereof. In the right and left side edges of the liquid-impermeable sheet 1013, expanded elastic members 1012 are disposed. The liquid-impermeable sheet 1013 extends to the outside of the side portion of the absorber 1005. The liquid-impermeable sheet 1013 and the exterior sheet 1011 are bonded to each other with a heat-sensitive adhesive (hereinafter, HMA) or the like. [0157] The absorber 1005 is a laminate having liquid absorption and retention properties. The absorber 1005 is composed of a mixture of absorbent pulp and a high absorbent polymer. [0158] In the back-side region S11, a waist flap portion 1014 is provided in the outside of each side flap portion 1010 in the width direction. The waist flap portion 1014 is made of a liquid-permeable or impermeable sheet. The waist flap portion 1014 includes a locking member 1015 such as a mechanical lock or adhesive tape so as to fix the absorbent article 1001 B in the front side part. [0159] In this embodiment, the exterior sheet 1011 and the liquid-impermeable sheet 1013 are bonded to each other with HMA or the like to form the backsheet 1004. Thereafter, two polyurethane elastic yarns 470dtex as the elastic members 1012 are expanded 2.2 times and disposed on the exterior sheet 1011. The elastic yams are wrapped around by the exterior sheet 1011. Furthermore, in a central part of each side flap portion 1010 in the longitudinal direction, the portion where the exterior sheet 1011 overlaps the liquid-impermeable sheet 1013 is subjected to the stretching processing in the width direction W. The absorber 1005 is then disposed on the backsheet 1004 after the stretching processing. The diaper 1001B may be formed other than the above processing. [01601 Next, the highly moisture-permeable regions 1006 provided in the side flap portions 1010 are described. As shown in Figs. 22 and 23, the highly moisture-permeable regions 1006 are formed in the backsheet 1004 composed of the liquid-impermeable sheet 1013 and the exterior sheet 1011. The highly moisture-permeable regions 1006 are provided between the end edges of the side flap portions 1010 and the side edges of the absorber 1005. The highly moisture-permeable regions 1006 are formed by performing the stretching processing for the backsheet 1004. 27 G20801OO(JUN-048-PCT) Eng. Spec_Final.doc [0161] Fig. 25 shows a portion subjected to the stretching processing. In the case of the diaper 1001B having a whole length of 470 mm in the longitudinal direction L, the backsheet 1004 is subjected to the stretching processing in a 20 mm wide portion outside in the width direction starting from a position 5 mm away from each side edge of the absorber 1005. The absorber 1005 is subjected to the stretching processing over the whole length in the longitudinal direction L. The length of the portions subjected to the stretching processing in the longitudinal direction L is not a restriction requirement because the design of the diaper varies depending on the length of the diaper, width of the absorber 1005, and the like. Preferably, in the case of an open-type diaper or pant-type diaper, the highly moisture-permeable regions 1006 are provided over the whole length of the side flap portions provided in the longitudinal direction (over front and back panels in the case of the pant-type diaper). [0162] The exterior sheet 1011 and the liquid-impermeable sheet 1013 are bonded to each other with HMA or the like into the backsheet 1004, which is then stretched using the stretching apparatus shown in Fig. 27. [0163] As shown in Fig. 27, a stretching apparatus 1030 includes a pair of stretching blade units 1031 which face each other and can be meshed with each other. Each of the stretching tooth units 1031 has a 2.5 mm blade depth, a 1.25 mm pitch between a pair of upper and lower blades, and 17 upper and lower blades. The stretching apparatus 1030 performs the stretching processing for a part of each side flap portion 1010 with a temperature of the stretching blade units set to 90 0 C. With such stretching processing, the highly moisture-permeable regions 1006 are 1.8 times longer than the original width before stretching. Specifically, the highly moisture-permeable regions 1006, which have an average permeability of 1935 (Pa-24hrs) before stretching, have an average permeability of 3191 (Pa-24hrs), which is increased by a factor of about 1.65 (see Table 1). [0164] At the stretching processing, the blades are heated to soften the backsheet 1004. This facilitates reducing the basis weight, and pin holes are therefore less likely to occur. Proper heating temperature is preferably 20 to 30 degrees lower than the melting point of the material. If the liquid-impermeable sheet 1013 is heated at a temperature above the melting point of the material thereof, the liquid-impermeable sheet 1013 is molten and is subject to tears. Heating to such a temperature is not preferable. [0165] The backsheet 1004 is formed by bonding a moisture permeable film (the liquid-impermeable sheet 1013) with a basis weight of 22.0 g/m 2 and a liquid-permeable SMS (the exterior sheet 1011) with a basis weight of 13 g/m 2 to each other with HMA applied in a diameter of 15 mm and a basis weight of 5 g/m 2 using spiral spray. Table 1 shows the results of stretching. 28 G20801OO(JUN-048-PCT)_Eng. SpecFinal.doc Table 1 n=1 n=2 n=3 Average Before Initial 71.39 64.12 66.15 Increasing weight (g) Moisture Weight (g) 65.53 59.06 60.67 Permeability after 24 hrs. (Before Weight 5.85 5.06 5.49 Stretching) difference (g) Moisture 2071.4 1791.6 1941.8 1934.9 permeability (Pa-24hrs) After Initial 66.65 67.96 67.41 Increasing weight (g) Moisture Weight (g) 57.58 59.10 58.29 Permeability after 24 hrs. (After Weight 9.07 8.86 9.11 Stretching) difference (g) Moisture 3210.8 3136.6 3224.8 3190.8 permeability (Pa-24hrs) [0166] Figs. 25 and 26 show the distance for stretching (increasing the permeability). The width of each side flap portion 1010 subjected to the stretching processing is indicated by a width X from the side edge of the absorber 1005 to the vicinity of the inside of the elastic member 1012 located closest to the absorber 1005 in the side flap portion 1010 when the diaper 1001B is opened (Fig. 25). A width Y is a width from the side edge of the absorber 1005 to the vicinity of the inside of the elastic member 1012 located closest to the absorber 1005 in the side flap portion 1010 when the crotch part of the side flap portion 1010 is expanded in the width direction W (Fig. 26). Preferably, the width Y is 1.5 to 3.0 times the width X. [0167] If the width Y is less than 1.5 times the width X, the small stretched width of the highly moisture-permeable region 1006 cannot provide enough height of the standing side flap portion 1010 when the diaper is wom. This causes a gap between the skin and the portion where the elastic members 1012 are provided, and the gap can leak excretion. [0168] If the width Y is more than 3.0 times the width X, because of the large stretched width of the highly moisture-permeable region 1006, the moisture permeability is increased by the stretching, and the materials are therefore more likely to be damaged. Accordingly, material defects including tears and holes are highly likely to occur. If the material is broken, the broken part could leak excretion. 29 G20801OO(JUN-048-PCT)_Eng. SpecFinal.doc [0169] As for the moisture permeability in the stretched region (highly moisture-permeable region 1006), the moisture permeability after the stretching processing is preferably 1.3 to 2.5 or more times the moisture permeability before the stretching process. In this case, the moisture permeability before the stretching processing means the moisture permeability in the lower surface of the absorber in other words. When the moisture permeability after the stretching processing is less than 1.3 times the moisture permeability before the stretching processing, the small change in moisture permeability makes very little difference in the highly moisture-permeable regions 1006, thus resulting in a small effect on reducing the damp feeling in the diaper. [0170] Preferably, the material of the liquid-impermeable sheet 1013 suitable for the stretching processing has a film fracture elongation of 750% or more. Films with a film fracture elongation of less than 750% are subject to pin holes at the stretching process. The pin holes could sometimes cause leakage. [0171] In the above embodiment, the side flap portions 1010 are subjected to the stretching processing, and the backsheet 1004 is extended by the stretched width. As a result, the micropores by the filler are enlarged, so that the highly moisture-permeable regions 1006 subjected to the stretching processing have higher moisture permeability. The highly moisture-permeable regions 1006 therefore have a lower basis weight of the material and higher moisture permeability than those of the other region not subjected to the stretching processing (a so-called increased in moisture permeability). Moreover, when the highly moisture-permeable regions 1006 are increased in moisture permeability, the material constituting the highly moisture-permeable regions 1006 are softened. Furthermore, in the diaper 1001 B, the plane where the elastic members 1012 are placed can be held higher than the surface of the liquid-permeable sheet by the stretched width. As shown in Fig. 24, therefore, the diaper 1001 B forms a larger pocket 1016 accommodating body fluid than that of a diaper not subjected to the stretching processing. [0172] As described above, according to Embodiment 2-2, in the diaper 1001 B, the backsheet 1004 is formed by bonding the liquid-impermeable sheet 1013 and the exterior sheet 1011 to each other, and the highly moisture-permeable regions 1006, which are increased in moisture permeability, are disposed in the side flap portions 1010 on the sides of the absorber 1005 in the backsheet 1004. The diaper 1001 B therefore has a structure in which the side flap portions 1010 are composed of a film material and are increased in resistance to water pressure. The diaper 1001B can be prevented from leaking body fluid. In addition, the diaper 1001 is increased in breathability and moisture permeability due to the effect of increased moisture permeability. It is therefore possible to prevent damp feeling in the diaper 1001 B which will damage the skin. [0173] Furthermore, according to Embodiment 2-2, the soft regions are formed by the stretching processing 30 G20801OO(JUN-048-PCT)_Eng. Spec_Final.doc in the side flap portions 1010 located in the inner surface of the diaper 1001B. The inner surface of the diaper 1001 B is soft, and the diaper 1001 B can reduce uncomfortable feeling in wearing than a diaper not subjected to the stretching processing. [0174] Moreover, since the inner surface of the diaper 1001 B is soft, the elastic members 1012 well stretch, and the side flap portions 1010 can easily stand up in the diaper. The diaper 1001B snugly fit to the body and is less likely to leak excretion. [0175] Still furthermore, in the diaper 1001 B, the highly moisture-permeable regions are not disposed in the lower surface of the absorber 1005 to which the highest body pressure is applied when the diaper 1001B is wom, and the lower surface of the absorber 1005 has higher resistance to water pressure than the highly moisture-permeable regions 1006. Accordingly, even when the diaper 1001B is wom for a long time, the lower surface of the absorber 1005 the diaper 1001 B does not exude excretion and leak moisture, thus preventing underwear and bedclothes from being soaked. [0176] According to Embodiment 2-2, in the diaper 1001B, the same material continuous in the width direction W is disposed in the side flap portions 1010 and in the lower surface of the absorber 1005 while having different effects in the side flap portions 1010 and in the lower surface of the absorber 1005. Specifically, the side flap portions 1010 are excellent in breathability and moisture permeability while the lower surface of the absorber 1005 is excellent in resistance to water pressure. [0177] In this embodiment, the liquid-impermeable sheet 1013 and the exterior sheet 1011 constituting the backsheet 1004 are preferably bonded with HMA using a spiral spray. The materials can be partially bonded with HMA using the spiral spray, and the density of bonded area is low. The bonded area of low density does not inhibit so much the liquid-impermeable sheet 1013 from extending at stretching. The stretching processing is less likely to cause material defects. In the case where the bonded area of the bonded materials are of high density like curtain coating HMA, the liquid-impermeable sheet 1013 at stretching is inhibited from stretching by the exterior sheet 1011. In short, the stretching processing with the bonded area of high density is more likely to cause material defects. In the case of bonding with HMA, HMA can be heated before stretching to be softened for use. [0178] The elastic members 1012 only need to be disposed in a region of each side flap portion 1010 in the backsheet 1004 which is not subjected to the stretching processing. The number of elastic members 1012 is not limited and may vary on the function and design of the diaper. When a plurality of elastic members 1012 are disposed in each side flap portion 1010 and the region where the elastic members 1012 are disposed is shaped in a plane and is brought into contact with the wearer, the elastic member 1012 located closest to the absorber 1005 is preferably disposed in a non-highly moisture-permeable region near the boundary between the highly moisture-permeable region 1006 and the non-highly moisture-permeable region. 31 G20801OO(JUN-048-PCT)_Eng. Spec_Final.doc [0179] This facilitates forming a folding line as the boundary between the highly moisture-permeable region 1006 and the non-highly moisture-permeable region because of the difference in rigidity between the highly moisture-permeable region 1006 and the non-highly moisture-permeable region. The non-highly moisture-permeable region is raised at this folding line, so that the region of each side flap portion 1010 where the elastic member 1012 are disposed fits to the wearer's skin without wrinkles. The diaper 1001B can be increased in sealability. [0180] In Embodiments 2-3 to 2-6 below, the different points from Embodiments 2-1 and 2-2 are mainly described, and the redundant description is omitted. [0181] (Embodiment 2-3) Fig. 28 shows Embodiment 2-3 of the present invention. In a diaper 1001C of this embodiment, the backsheet 1004 is formed by bonding the liquid-impermeable sheet 1013 and the exterior sheet 1011 to each other. The topsheet 1003 covers the absorber 1005 and extends laterally. The topsheet 1003 is made of a hydrophilic liquid-impermeable sheet. The topsheet 1003, liquid-impermeable sheet 1013, and exterior sheet 1011 are bonded. The bonded portions are subjected to the stretching processing (increased in moisture permeability). In short, the highly moisture-permeable regions 1006 are formed in the liquid-impermeable sheet 1013, exterior sheet 1011, and the topsheet 1003. [0182] In the diaper 1001C having such a structure, body fluid flown out from side portions of the absorber 1005 to the highly moisture-permeable regions 1006 can be again introduced to the absorber 1005 by the liquid-permeable sheet (the topsheet 1003). [0183] (Embodiment 2-4) Fig. 29 shows Embodiment 2-4 of the present invention. In a diaper 1001D of this embodiment, two side flap portions 1017 and 1018 are provided on each side and are individually subjected to the stretching processing (increased in moisture permeability). With the two side flap portions 1017 and 1018 disposed in each side of the absorber 1005, the diaper 1001D can be doubly prevented from leaking. Moreover, the liquid-impermeable sheet 1013 constituting the backsheet 1004 is partially covered with the side flap portions 1018. The diaper 1001D therefore has soft texture. [0184] (Embodiment 2-5) Fig. 30 shows Embodiment 2-5 of the present invention. In a diaper 1001E of this embodiment, the side flap portions 1010 are formed so as to incline inwardly and are subjected to the stretching processing (increased in moisture permeability). In the diaper 1001E of such a structure, the surface of the absorber 1005 is covered with the side flap portions 1010, thus reducing the area of the absorber 1005 coming into contact with the wearer's skin. Accordingly, less excretion gets back 32 G20801OO(JUN-048-PCT)_Eng. SpecFinal.doc to the wearer's skin. [0185] (Embodiment 2-6) Fig. 31 shows Embodiment 2-6 of the present invention. In a diaper 1001 F of this embodiment, as for central and end portions 1006a and 1006b of the highly moisture-permeable region 1006 which are disposed in the longitudinal direction L, the area with increased moisture permeability is wider in the central portion 1006a than in the end portions 1006b. Accordingly, the width of the pocket in the central portion 1006a is larger than that in the end portions 1006b. The diaper 1001 F can hold large capacity under the crotch where excretion is more likely to pool. The diaper 1001F can be therefore prevented from leaking. [0186] For processing to implement this embodiment, the end portions 1006b and central portion 1006a are subjected to the stretching processing with pressing blades of different heights. Specifically, the height by which the blades are pressed in the central portion 1006a is set higher than that in the end portions 1006b, so that the central portion 1006a has a higher moisture permeability than that of the end portions 1006b. Alternately, the area increased in moisture permeability in the central portion 1006a is set wider in the width direction W than that in the end portions 1006b. In other words, the increasing in moisture permeability is performed for different areas between the central portion 1006a and each end portion 1006b, so that the central portion 1006a has higher moisture permeability than the end portions 1006. [0187] (Other Embodiments) The diaper in this embodiment includes a portion having moisture permeability increased (subjected to the stretching processing) on each side of the absorber 1005 but is not limited to an open-type diaper. The diaper of this embodiment may be a pant-type in which the diaper body is folded at the longitudinal center and both sides on back and front sides are locked and fixed. Such a diaper can hold large space under the crotch where excretion is more likely to pool. The diaper can be therefore prevented from leaking. [0188] The present invention is not limited to the aforementioned diapers and is applicable to absorbent articles such as sanitary napkins and urine absorbing pads. [0189] In this embodiment, the liquid-impermeable sheet 1013 used in the sheet 1004 is made of a film composed of polyethylene containing about 50 wt% calcium carbide as a filler. Such a film may be a film which includes micropores formed by stretching at the process of manufacturing the film and is moisture permeable before increasing the moisture permeability at the processing of the diaper. [0190] Similarly, such a film can be a moisture-impermeable film which is made of polyethylene with a basis 33 G2080 1 OO(JUN-048-PCT)_Eng. SpecFinal.doc weight of 15 to 40 g/m 2 containing 20 to 70 wt% calcium carbide as a filler and is substantially not extended during the manufacturing processing of the film. In this case, the backsheet 1004 is stretched by a stretched width by the stretching processing performed during diaper processing, so that micropores are formed by the filler to give the moisture permeability to the film. [0191] In a portion of the lower surface under the absorber 1005 subjected to the body pressure, the film does not include micropores and is accordingly capable of holding higher resistance to water pressure. It is therefore possible to effectively prevent liquid from exuding through the liquid-impermeable sheet 1013. [0192] In this embodiment, the film is a moisture-permeable film. The resin used in the moisture-permeable film is a sheet of polyethylene resin, polypropylene resin, or fluorine resin formed into a thickness of 20 to 40 pm by hot stretching film formation. [0193] This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2008-093816 filed on March 31, 2008; the entire contents of which are incorporated herein by reference. [0194] (Embodiment 3-1) [Background Art] Diapers forming a so-called pocket between wearer's skin and crotch part have been known (Patent Literature 4, for example). As shown in Fig. 32 (a), a diaper 2100 includes an absorbent body 2101 composed of a liquid-permeable topsheet 2101a, a liquid-impermeable backsheet (not shown), and an absorber 2101c absorbing and retaining liquid. The absorber 2101c is disposed between the topsheet 2101a and the backsheet (not shown). When the diaper is wom, the absorbent body 2101 extends across a back-side region S21, a crotch region S22, and a front-side region S23 in a longitudinal direction from the back side to the front side and covers the wearer from the back side to front side with the crotch being centered. On both sides of the absorbent body 2101 in the width direction, the topsheet 2101a and the backsheet (not shown) are extended to provide side flap portions 2110. In the crotch region S22, an expanded elastic member 2120 is provided along the longitudinal direction at an outer edge of each side flap portion 2110. In the front-side region S23, a folded portion 2130 is provided in each side flap portion 2110. [0195] When a wearer wears the diaper 2100 of the conventional example, the outer edges of the side flap portions 2110 come into close contact with wearer's legs due to contraction of each elastic member 2120. Moreover, for the width dimension of each side flap portion 2110 is larger in the crotch region S22 than that in the front-side region S23, space, or a so-called pocket is formed under the wearer's crotch. This pocket can surely hold urine, faces, and the like excreted from the wearer without causing side leakage. 34 G2080100(JUN-048-PCT)_Eng. Spec_Final.doc [0196] A diaper 2150 of another conventional example is disclosed in Patent Literature 5. As shown in Fig. 32 (b), the diaper 2150 includes an absorbent body 2151 composed of a liquid-permeable topsheet 2151a, a liquid-impermeable backsheet 2151b, and an absorber 2151c absorbing and retaining liquid. The absorber 2151c is disposed between the topsheet 2151a and the backsheet 2151b. When the diaper is wom, the absorbent body 2151 extends across the back-side region S21, the crotch region S22, and the front-side region S23 in a longitudinal direction from the back side to the front side and covers the wearer from the back side to front side with the crotch being centered. On both sides of the absorbent body 2151 in the width direction, a pair of expanded elastic members 2152 are provided. Each elastic member 2152 is provided so as to curve outward in the crotch region S22. The distance between the pair of elastic members 2151 is set narrow in the back and front-side regions S21 and S23 and set wide in the crotch region S22. [0197] When a wearer wears the diaper 2150 of the another conventional example, the outer edges of the absorbent body 2151 in the crotch region S22 come into close contact with wearer's legs due to contraction of the elastic members 2152. Moreover, since the distance between the pair of elastic members 2152 is wide in the crotch region S22 of the absorbent body 2151, space, or a so-called pocket is formed under the wearer's crotch. Similarly to the aforementioned conventional example, this pocket can surely hold urine, faces, and the like excreted from the wearer without causing side leakage. [0198] (Patent Literature 4) Japanese Patent Laid-open Publication No. 62-199802 (Page 6, Figs. 4 and 5) (Patent Literature 5) Japanese Patent Laid-open Publication No. 4-242645 (Page 8, Figs. 1 and 2) [Disclosure of the Invention] However, in the aforementioned two conventional examples, the diapers 2100 and 2150 require excessive materials in the width direction thereof compared to a diaper not forming a pocket in order to form the pocket in the crotch region S22 when the diaper is wom. [0199] Moreover, in the former conventional example, since the folded portion 2130 is provided in each side flap portion 2110, processing at manufacturing is troublesome, thus increasing the manufacturing cost. [0200] In the latter conventional example, since the pair of elastic members 2152 need to be provided in a curve, processing at manufacturing is troublesome, thus increasing the manufacturing cost. [0201] An object of the present invention is therefore to provide an absorbent article which forms a so-called pocket under the wearer's crotch, the absorbent article being capable of being manufactured with less materials and easier processing at lower cost accordingly. 35 G20801OO(JUN-048-PCT)_Eng. Spec Final.doc [0202] An aspect of the present invention to achieve the aforementioned object is an absorbent article (for example, a diaper 2001A) including: an absorbent body (an absorbent body 2002) composed of at least a liquid-permeable topsheet (a topsheet 2003), a liquid-impermeable backsheet (a backsheet 2004), and an absorber (an absorber 2005) disposed between the topsheet and the backsheet and configured to absorb and retain liquid, the absorbent body having a back-side region (back-side region S21), a crotch region (a crotch region S22), and a front-side region (a front-side region S23) located in a longitudinal direction (a longitudinal direction L) from the back side to the front side when the absorbent article is wom; a pair of right and left side flap portions (side flap portions 2010) provided on both sides of the absorbent body in the width direction (a width direction W); and a pair of elastic members (for example, elastic members a) provided in an extended state in the longitudinal direction for each side flap portion at least in the crotch region. In the absorbent article, crotch-side stretched regions (for example, crotch-side stretched regions 2013) expanded in the width direction are provided in each side flap portion in the crotch region between the absorbent body and the elastic member located at the outermost position. [0203] According to the aspect of the present invention, when the wearer wears the absorbent article, the outer edges of the side flap portions 2110 come into close contact with wearer's legs due to contraction of the elastic members. Moreover, since the expandable width dimension of each side flap portion is larger in the crotch region than that in the front and back-side regions due to the pair of crotch-side stretched regions, a so-called pocket is formed under the wearer's crotch. Each crotch-side stretched region can be formed with a material of a same width as that of a diaper not forming a so-called pocket in the crotch region because the crotch-side stretched region is provided by stretching a part of each side flap portion in the crotch region in the width dimension. Moreover, the pocket can be formed under the wearer's crotch without providing a folded portion in each side flap portion or without providing a curved elastic member in each side flap portion. As described above, it is possible to reduce used amounts of materials, facilitate processing at manufacturing, and reduce the manufacturing cost accordingly. [0204] Moreover, the portion of each side flap portion covering the wearer's leg near his/her crotch corresponds to the crotch-side stretched region which is thin and soft. Accordingly, the side flap portions have advantages of providing less uncomfortable feeling, well following the movement of wearer's legs, easily standing relative to the absorbent body, and bringing the outer edges thereof close contact with the wearer's legs without being excessively tightened. [0205] [Modes for Carrying out the Invention] Figs 33 to 38 show Embodiment 3-1 of the present invention. Fig. 33 is a plan view of the developed state of the diaper 2001A. Fig. 34 is a cross-sectional view of Fig. 33 taken along a line A2-A2. Fig. 35 is a cross-sectional view of Fig. 33 taken along a line B2-B2. Fig. 36 is a cross-sectional view of the diaper 2001A in use. Fig. 37 is a cross-sectional view of a main portion 36 G20801OO(JUN-048-PCT)_Eng. Spec_Final.doc of a stretching machine. Fig. 38(a) is a plan view of the diaper 2001A before each side flap portion in the crotch region is pulled outward at the center. Fig. 38(b) is a plan view of the diaper 2001A with respective central edges of the side flap portions in the crotch region being pulled outward. [0206] As shown in Figs. 33 to 35, the diaper 2001 A as an absorbent article includes the absorbent body 2002, a pair of right and left side flap portions 2010 provided on the both sides of the absorbent body 2002 in the width direction, a pair of back-side waist flap portions 2020 provided on both sides of the pair of side flap portions 2010 in the width direction W on the back side, and a pair of front-side waist flap portions 2021 provided on both sides of the pair of side flap portions 2010 in the width direction W on the front side. [0207] The absorbent body 2002 includes at least a liquid-permeable topsheet 2003, a liquid-impermeable backsheet 2004, and an absorber 2005 disposed between the topsheet 2003 and the backsheet 2004 and configured to absorb and retain liquid. The front and back sides of the diaper 2001A are determined. In the diaper 2001A, the back-side region S21, the crotch region S22, and the front-side region S23 are sequentially provided in the longitudinal direction L from the back side to the front side. When the diaper 2001A is wom, the absorbent body 2002 extends across the back, crotch, and front-side regions S21 to S23 from the back to front side and covers the back, crotch, and front sides of the wearer. [0208] The both edges of the topsheet 2003 in the width direction W are folded so as to wrap around the absorber 1005. The folded portions of the topsheet 2003 and the absorber 2005 are bonded to the backsheet 2004 with a glue such as a hot melt adhesive. The topsheet 2003 is made of hydrophilic nonwoven fabric, woven fabric, perforated plastic film, perforated hydrophobic nonwoven fabric, laminated nonwoven fabric manufactured by spunbond/meltblown/spunbond (hereinafter, referred to as SMS) with a basis weight of 10 g/m 2 , or the like. [0209] The backsheet 4 is made of moisture-permeable or moisture-impermeable film, a sheet composed of such permeable or impermeable film bonded to nonwoven fabric, or the like. The absorber 2005 is a laminate including liquid absorption and retention characteristics. The absorber 2005 is formed by mixing absorbent pulp and a highly absorbent polymer. [0210] The pair of side flap portions 2010 are composed of portions of the backsheet 2004 extended from the both sides of the absorbent body 2002 in the width direction W and portions of the liquid-impermeable exterior sheet 2011. The exterior sheet 2011 is laid on the rear surface of the absorbent body 2002 and the backsheet 2004. [0211] The backsheet 2004 and the exterior sheet 2011 are bonded with glue such as a hot melt adhesive. 37 G2080100(JUN-048-PCT)_Eng. SpecFinal.doc The exterior sheet 2011 is formed so as to be longer in the width direction W than the backsheet 2004. [0212] Four elastic members 2012a to 2012d extended in the longitudinal direction L are provided in the entire area of each side flap portion 2010 in the crotch region S22 and in partial areas of each side flap portion 2010 in the back and front-side regions S22 and S23 continuous to the crotch region S22. [0213] On each side of the exterior sheet 2011, which is longer in the width direction W than the backsheet 4, the outer three elastic members 2012a to 2012c are provided. The elastic member 2012d located at the innermost position is disposed at the substantially center between a corresponding side edge of the absorbent body 2 and the elastic member 2012a located at the outermost position. The elastic member 2012d is provided between the exterior sheet 2011 and the backsheet 2004. Each of the elastic members 2012a to 2012d is made of polyurethane elastic yam, for example. [0214] In the crotch region S22, a crotch-side stretched region 2013 stretched in a width direction W is provided in each side flap portions 2010 between the absorbent body 2002 and the elastic member 2012a located at the outermost position. Specifically, each crotch-side stretched region 2013 is provided between the absorbent body 2002 and the third elastic member 2012c from the outside. Each crotch-side stretched region 2013 is a region formed to have a lower weight than the other region by stretching. In the crotch-side stretched region 1013, dense portions (no referential numbers) stretched a small amount and low-dense portions (no referential numbers) stretched a large amount are alternately provided in the width direction W of the side flap portions 2010. Each crotch-side stretched region 2015 is stretched by a factor of 1.5 to 3.0 compared to the original width before stretching. [0215] Each crotch-side stretched region 2013 has such a transparency that excretion inside is visible from the outside when the diaper is wom. The transmittance of each crotch-side stretched region 2013 is a transmittance from the outside to the inside. The light transmittance thereof is increased by not less than 3% by the stretching process. If the light transmittance is not less than 61 % (measured by JIS K7105), excretion inside is visible from the outside. [0216] Moreover, each crotch-side stretched region 2013 of this embodiment is provided from the absorbent body 2002 to the elastic member 2012a located at the outermost position in the width direction W of the side flap portions 2010. Each crotch-side stretched region 2013 is provided in the entire range of the crotch region S22 in the longitudinal direction L of the side flap portions 2010. Each crotch-side stretched region 2013 is not extended to the back or front-side regions S21 and S23 in this embodiment. The specific method of manufacturing the crotch-side stretched regions 2013 is described in detail below. 38 G2080100(JUN-048-PCT)_Eng. SpecFinaldoc [0217] The waist flap portion is composed of a pair of back-side waist flap portions 2020 and a pair of front-side waist flap portions 2021. One end of each of the pair of back-side waist flap portions 2020 is fixed to one of the pair of side flap portions 2010 in the back-side region S21. A locking portion 2022 is provided at a top end of each back-side waist flap portion 2020. [0218] Each locking portion 2022 is a hook-and-loop fastener for locking with mechanical locking force or adhesive tape for locking with adhesive force. When the locking portion 2022 is a hook-and-loop fastener, each front-side waist flap portion 2021 is made of a sheet material having nonwoven fabric at least in the surface. [0219] Next, the method of manufacturing the crotch-side stretched regions 2013 is briefly described. The side flap portions 2010 are formed by bonding the backsheet 2004 and the exterior sheet 2011 with a heat-sensitive adhesive (for example, hot melt adhesive or the like. Hereinafter, referred to as HMA) applied in a diameter of 15 mm and a basis weight of 5 g/m 2 using spiral spray. The backsheet 2004 is made of a non-breathable sheet with a basis weight of 23.5 g/m 2 . The exterior sheet 2011 is made of SMS with a basis weight of 13 g/m 2 . [0220] As shown in Fig. 37, a stretching machine 2030 forming the crotch-side stretched regions 2013 includes a pair of stretching blade units 2031 which face each other and can be meshed with each other. Each of the stretching blade units 2031 is configured to have a 2.5 mm blade depth, a 1.25 mm pitch between a pair of blades, and 17 blades. The stretching machine 2030 performs the stretching process at a temperature of the stretching blade units 2031 set to 1 00*C. With such a stretching process, the crotch-side stretched regions 2013 can be stretched by a factor of 1.8 compared to before stretching. [0221] Stretching with the stretching machine 2030 alternately provides dense portions stretched a small amount and low-dense portions stretched a large amount in the side flap portions 2010 in the width direction W. [0222] The stretching ratio can be changed by properly changing the aforementioned conditions. Width 22 is 1.5 to 3.0 times width 21 of the crotch-side stretched region 2013 of Fig. 38(a) before central part of the side flap portion 2010 in the crotch region S22 is pulled outward. [0223] The width W22 is a width of the crotch-side stretched region 2013 with respective central edges of the side flap portions 2010 in the crotch region S22 being pulled outward. Specifically, the width W22 can be expanded by the stretching ratio of 1.5 to 3.0 with respect to the width W21. Each side flap portion 2010 can be expanded in the crotch region S22 by the stretching ratio of 1.5 to 3.0 at 39 G2080 OO(JUN-048-PCT)_Eng. SpecFinal.doc maximum with respect to the width dimension in the back- or front-side region S21 or S23. [0224] The transmittance from the outside to the inside varies depending on the type of the sheet material of the side flap portions 2010. The stretching amount is therefore adjusted depending on the type of the sheet material to obtain the transmittance from the outside to the inside. [0225] When a wearer wears the diaper 2001A of the aforementioned configuration, as shown in Fig. 36, the outer edges of the side flap portions 2010 come into close contact with wearer's legs due to contraction of the elastic members 2012a and 2012b. Moreover, since the maximum expandable width dimension of each side flap portion 2010 is larger in the crotch region S22 than in the front- and back-side regions S21 and S22 due to the pair of crotch-side stretched regions 2013, a so-called pocket P is formed under the wearer's crotch. [0226] The crotch-side stretched regions 2013 are formed by stretching each side flap portion 2010 in the crotch region S22 in the width direction W. Each crotch-side stretched region 2013 can be made of a material of a same width as that of a diaper not forming a so-called pocket P in the crotch region S22. [0227] Moreover, the diaper 2001A can form the pocket P under the wearer's crotch without providing a folded portion in each side flap portion 2010 or without providing the elastic members 2012 in a curved fashion in each side flap portions 2010. The diaper 2001A can be made of less material and manufactured by simpler processing at the manufacturing at lower manufacturing cost accordingly. [0228] Moreover, in the diaper 2001A, the portion of each side flap portion covering the wearer's leg near his/her crotch corresponds to the crotch-side stretched region 2013, which is thin and soft. Accordingly, the diaper 2001 A has advantages of providing less uncomfortable feeling of wearing, improving in ability of following the movement of wearer's legs, easily standing relative to the absorbent body 2002, and bringing the outer edges of the side flap portions close contact with the wearer's legs without excessively tightening the same. [0229] In this embodiment, since each crotch-side stretched region 2013 is provided in a half on the absorbent body 2002 side of the central line dividing in halves in the width direction W a region between the side edge of the absorbent body 2002 and the elastic member 2012a, which is located at the outermost position, the diaper 2001A has the following advantages, too. When the wearer wears the diaper 2001A, the diaper 1A bends at the positions where the rigidity changes, or at the boundaries between the absorbent body 2002 and the side flap portions 2010. In this embodiment, the boundaries between the absorbent body 2002 and the side flap portions 2010 are located at the respective crotch-side stretched regions 2013, which are made flexible, thus providing good standing 40 G20801OO(JUN-048-PCT)_Eng. SpecFinal.doc properties. The so-called pocket P can be therefore easily formed. [0230] In this embodiment, the diaper 2001A includes the back and front-side waist flap portions 2020 and 2021 protruding from the both sides of the pair of side flap portions 2010 in the back- and front-side regions S21 and S23, respectively. Each crotch-side stretched region 2013 is provided only within the crotch region S22. Accordingly, when the diaper 2001A is wom using the back- and front-side waist flap portions 2020 and 2021, the tightening force of the back- and front-side waist flap portions 2020 and 2021 does not directly act on the crotch-side stretched regions 2013 and does not adversely affect formation of the pocket in the crotch region S22 of the diaper 2001A, thus not reducing the strength of the diaper 2001 A. [0231] In this embodiment, since each crotch-side stretched region 2013 has such a transparency that excretion inside is visible from the outside when the diaper 2001A is in use, the presence of excretion within the diaper 2001A can be checked through the crotch-side stretched regions 2013. It is therefore possible to easily determine the time for replacement of the diaper 2001 A and the like. [0232] In this embodiment, each crotch-side stretched region 2013 includes the dense portions stretched a small amount and low-dense portions stretched a large amount alternately provided in the width direction W of the side flap portion 2010. Accordingly, each crotch-side stretched region 2013 is alternately folded in opposite directions due to the dense and low-dense portions in the manufacturing process of the diaper 2001A. The outer edge of each side flap portion 2010 forms a straight line without protruding. The diaper 2001A can therefore be handled well at the manufacturing process, product packaging process, and the like. [0233] In this embodiment, each crotch-side stretched region 2013 is 1.5 to 3.0 times longer than that before stretched. If the stretching ratio of each crotch-side stretched region 2013 is less than 1.5, the height of the standing side flap portions 2010 is so small that the elastic members 2012 does not come into close contact with the skin. On the other hand, if the stretching ratio of each crotch-side stretched region 2013 exceeds 3.0, a lot of damage due to stretching could cause material defects such as tears and holes. [0234] By setting the stretching ratio of each crotch-side stretched region 2013 in a range of 1.5 to 3.0, a space, or a so-called pocket can be formed at the crotch region S22 of the diaper 2001 A without a fear of causing material defects. [0235] (Modifications of Embodiment 3-1) In Embodiment 3-1, each side flap portion 2010 is composed of two layers of the exterior sheet 2011 and backsheet 2004. However, each side flap portion 2010 may be composed of a single layer of 41 G2080100(JUN-048-PCT)_Eng. Spec_Final.doc the backsheet 2004. If each side flap portion 2010 is composed of a single layer of the exterior sheet 2011, the necessary amount of the exterior sheet 2011 can be reduced. [0236] Alternatively, each side flap portion 2010 may be composed of three layers of the exterior sheet 2011, the backsheet 2004, and the topsheet 2003. If each side flap portion 2010 is composed of three layers of the exterior sheet 2011, the backsheet 2004, and the topsheet 2003, the crotch-side stretched regions 2013 of the side flap portions 2010 can be strengthened. [0237] The backsheet 2004 may be composed of sheet materials different in a part corresponding to the crotch-side stretched regions 2013 and the other part. For example, if the part of the backsheet 2004 corresponding to the crotch-side stretched region 2013 is made of a sheet material suitable for stretching processing while the other part is made of a sheet material suitable as a backsheet of the absorbent body 2002, the backsheet 2004 has excellent properties in the stretching processing and liquid impermeability. [0238] (Embodiment 3-2) Fig. 39 is a cross-sectional view of a diaper 2001 B according to Embodiment 3-2 of the present invention. [0239] As shown in Fig. 39, the diaper 2001 B according to Embodiment 3-2 differs from Embodiment 3-1 in terms of the configuration of the absorbent body 2002 and the configuration of a crotch-side stretched region 2013a of each side flap portion 2010. Specifically, the topsheet 2003 and the backsheet 2004 of the absorbent body 2002 are joined by a joint portion 2006 only at central part in the width direction W and are not joined at both ends in the width direction W. Each crotch-side stretched region 2013a is extended so as to overlap the absorbent body 2002 (to a region where the topsheet 3 and the backsheet 4 are not joined to each other). [0240] The other configuration is the same as that of Embodiment 3-1. The redundant description is omitted, and the same components in the drawing are given the same reference numerals for clarification. [0241] In this embodiment, since each crotch-side stretched region 2013a is extended so as to overlap the absorbent body 2002, the crotch-side stretched region 2013a can be configured to have large width dimension. In the diaper 2001 B, therefore, a space, or a so-called pocket formed at the crotch side of the diaper 1 D can be made deep. [0242] (Embodiment 3-3) 42 G20801OO(JUN-048-PCT)_Eng. Spec_Final.doc Fig. 40 is a cross-sectional view of a diaper 2001C according to Embodiment 3-3 of the present invention. [0243] As shown in Fig. 40, the diaper 2001C according to Embodiment 3-3 differs from Embodiment 3-1 in terms of only the configuration of each side flap portion 2010. Each side flap portion 2010 is divided into an inner flap portion 2010a and an outer flap portion 2010b in the outside of the side flap portion 2010 in the width direction W. The inner flap portion 2010a is made of a sheet material of good texture. At the end of the inner flap portion 2010a, the extended elastic member 2012e is provided. At the end of the outer flap portion 2010b, the extended elastic members 12a to 12c are provided. Each side flap portion 2010 doubly comes into close contact with the legs, and the diaper 2001C can more surely prevent side leakage. The diaper 2001C feels nice and soft since the inner flap portions 201 0a are made of a sheet material of good texture. [0244] The other configuration is the same as that of Embodiment 3-1. The redundant description is omitted, and the same components in the drawing are given the same reference numerals for clarification. [0245] (Modification of Embodiment 3-3) In Embodiment 3-3, the elastic members 2012a to 2012c and 2012e are provided at the ends of both the inner and outer flap portions 2010a and 2010b. However, in the diaper 2001C, the extended elastic members may be provided only at the end of the inner flap portion 201 Ga. In this case, the diaper 2001C has a so-called inwardly inclining three-dimensional gather structure. [0246] (Embodiment 3-4) Fig. 41 is a plan view of a developed state of a diaper 2001 D according to Embodiment 3-4 of the present invention. [0247] As shown in Fig. 41, the diaper 2001 D according to Embodiment 3-4 differs from Embodiment 3-1 in terms of only the configuration of each crotch-side stretched region 2013b. Each crotch-side stretched region 2013b is provided so that the width dimension thereof is larger at the center in the longitudinal direction L in the crotch region than at both ends in the longitudinal direction L in the side flap portion 2010 when the crotch-side stretched region 2013b is expanded in the width direction W. This is because the crotch-side stretched region 2013b varies in width dimension of the region subjected to the stretching processing in the longitudinal direction L. Specifically, the dimension of the stretched width at the center in the longitudinal direction L is set greater than that at each end in the longitudinal direction L. [0248] According to the diaper 2001 D, the ends of each crotch-side stretched region 2013b are constrained 43 G20801OO(JUN-048-PCT)_Eng. Spec_Final.doc to a portion not included in the crotch-side stretched regions 2013b. The pocket therefore has a shape with a height of the standing side flap portions set small at each end and largest at the center, so that the crotch-side stretched regions 2013b is reasonable for forming the pocket. [0249] Each crotch-side stretched region 2013b may be configured so that the width dimension of the region subjected to the stretching processing is constant in the longitudinal direction L and the stretching amount per unit length is varied in the longitudinal direction L. Each crotch-side stretched region 2013b is therefore provided so as to have a width dimension greater at the center in the longitudinal direction L than at each end in the longitudinal direction L when the crotch-side stretched regions 2013b are expanded (when the diaper 2001 D is wom). [0250] (Embodiment 3-5) Fig. 42 is a cross-sectional view of a diaper 2001 E according to Embodiment 4-5 of the present invention. [0251] As shown in Fig. 42, the diaper 2001 E according to Embodiment 3-5 differs from Embodiment 3-1 in terms of only the configuration of a pair of crotch-side stretched regions 2013A. Each crotch-side stretched region 2013A is extended not only in the crotch region S22 but also in both the back- and front-side regions S21 and S23. The ends of each crotch-side stretched region 2013A on the back and front sides do not reach the ends of the side flap portion 2010 on the back and front sides, respectively. [0252] According to this embodiment, the space or so-called pocket formed within the diaper 2001 E is formed not only in the crotch region S22 but also in the back- and front-side regions S21 and S23. The diaper 2001 E can temporarily hold a large amount of excretion and can be surely prevented from leaking excretion from the side. The diaper 2001 E is especially effective on preventing side leakage of both faces and urine. [0253] (Modifications of Embodiment 3-5) In a modification of Embodiment 3-5, each crotch-side stretched region 2013A is extended in each side flap portion 2010 from the crotch region S22 only to the back-side region S21. According to this modification, the space or so-called pocket formed within the diaper is formed in back-side region S21 as well as in the crotch region S22, and the diaper is especially effective on preventing side leakage of faces. [0254] In another modification of Embodiment 3-5, each crotch-side stretched region 2013A is extended in each side flap portion 2010 from the crotch region S22 only to the front-side region S23. According to this modification, the space or so-called pocket formed within the diaper is formed in front-side 44 G20801OO(JUN-048-PCT)_Eng. Spec_Final.doc region S23 as well as in the crotch region S22, and the diaper is especially effective on preventing side leakage of urine. [0255] (Others) In each embodiment, the four elastic members 2012a to 2012d are provided in each side flap portion 2010. However, the number and positions of the elastic members can be properly changed, and it is possible to provide only one or two elastic members in a side edge of each side flap portion 2010. [0256] Each embodiment shows the case where the present invention is applied to an open-type diaper, but the present invention can be applied to a pant-type diaper in a similar manner. The present invention can be also applied to absorbent articles as well as the diapers. [0257] The entire contents of Japanese Patent Application No. 2008-037916 filed on February 19, 2008 are incorporated herein by reference. [0258] (Embodiment 4-1) [Background Art] A conventional diaper of this kind is disclosed in Japanese Patent Laid-open Publication No. 2004-290400. As shown in Fig. 43, a diaper 3100 includes a absorbent article body 3101 composed of a liquid-permeable topsheet 3101a, a liquid-impermeable backsheet (not shown), and an absorber 3101c which is disposed between the topsheet 3101a and the backsheet and configured to absorb and retain liquid. [0259] Herein, in the diaper 3100, a "back side Ba" and a 'front side Fr" are determined. The back side Ba refers to a side which is on the back side of a wearer when the wearer wears the diaper 3100, and the front side Fr refers to a side which is on the wearer's front side when the diaper 3100 is wom. [0260] In the diaper 3100, a back-side region S1, a crotch region S2, and a front-side region S3 are sequentially provided in the longitudinal direction L from the back side Ba to the front side Fr. [0261] The absorbent article body 3101 is configured to cover the entire crotch part of the wearer from the wearer's back side to front side. [0262] On both sides of the absorbent article body 3101 in the width direction W, the topsheet 3101 a and the backsheet are extended to provide side flap portions 3110. 45 G20801OO(JUN-048-PCT)_Eng. Spec_Final.doc [0263] In each side flap portion 3110, elastic members 3111 stretched are provided in the longitudinal direction L of the absorbent article body 3101. [0264] In the back-side region S1, a pair of waist flap portions 3120 are provided in each side flap portion 3110. [0265] Each waist flap portion 3120 has a strip shape and is provided at a tilt (about 30 degrees) to a direction corresponding to the wearer's waistline direction (in the width direction W of the absorbent article body 3101). [0266] A locking member 3130 is attached to an end of each waist flap portion 3120. The locking member 3130 attached to respective ends of the waist flap portions 3120 is locked with the other waist flap portion 3120 to attach the diaper 3100 to the wearer's waist. [0267] Fixing portions 3140 are attached to the absorbent article body 3101 in the front-side region S3. The fixing portions 3140 are fixed to the waist flap portions 3120 wom on the wearer's waistline from the outside so that the absorbent article body 3101 covers the wearer's crotch part. [0268] In the diaper 3100, the pair of waist flap portions 3120 can be disposed so as to be inclined to the wearer' back side with respect to the wearer's waistline when the diaper 3100 is wom. The diaper 3100 fits snugly to the body. [0269] However, in the diaper 3100, the waist flap portions 3120 need to be arranged at an inclination to the direction corresponding to the wearer's waistline (in the width direction W of the absorbent article body 3101), thus leading to the problems of the complicated manufacturing process and increased material. [0270] [Disclosure of the Invention] An object of the present invention is to provide an absorbent article which fits snugly to a body and can be manufactured by a not-complicated manufacturing process without increasing the material. [0271] A first aspect of the present invention is an absorbent article in which back and front sides are determined and a back-side region, a crotch region, and a front-side region are sequentially provided in a longitudinal direction from the back side to the front side, the absorbent article including: an absorbent article body including a liquid-permeable topsheet, a liquid-impermeable backsheet, and 46 G20801OO(JUN-048-PCT)_Eng. SpecFinal.doc an absorber disposed between the topsheet and the backsheet and configured to absorb and retain liquid; a pair of side flap portions provided on both sides of the absorbent article body in the width direction and in the vicinity of both edges thereof outside in the width direction of the absorbent article body; and a pair of waist flap portions provided in the back-side region to protrude from the pair of side flap portions outward in the width direction of the absorbent article body. Each of the pair of waist flap portions is provided with a waistline stretched region, a dimension of each expanded waistline stretched region in the width direction of the absorbent article body is larger at an end on the front side than that at an end on the back side, and each of the waistline stretched regions is formed to reach respective ends of the pair of waistline flap portions on the front side. [0272] In the first aspect of the present invention, each of the waistline stretched regions may be provided in a range not reaching respective ends of the pair of waistline flap portions on the back side. [0273] In the first aspect of the present invention, each of the waistline stretched regions may be provided in a range reaching respective ends of the pair of waistline flap portions on the back side. [0274] In the first aspect of the present invention, each of the waistline stretched regions may be provided at respective bases of the pair of waistline flap portions. [0275] In the first aspect of the present invention, each waistline stretched region may be stretched by a factor of 1.1 to 3.0 at an end on the front side. [0276] [Modes for Carrying out the Invention] Figs. 44 to 50 show Embodiment 4-1 of the present invention. Fig. 44 is a plan view of a developed state of a diaper. Fig. 45 shows a cross-sectional view of Fig. 44 taken along a line A-A. Fig. 46 is a cross-sectional view of Fig. 44 taken along a line B-B. Fig. 47 is a cross-sectional view of Fig. 44 taken along a line C-C. Fig. 48 shows a cross-sectional view of a main portion of a stretching machine. Fig. 49 is a plan view of a stretching machine 3030 for stretching processing, that is, a waistline stretched region which is stretched. Fig. 50 is a side view of a diaper 1A in use, that is, an attached state of the diaper. [0277] As shown in Figs. 44 to 50, a diaper 3001A as an absorbent article includes an absorbent article body 3002, a pair of side flap portions 3010, a pair of back-side waist flap portions (waist flap portions) 3020, and a pair of front-side waist flap portions 3021. [0278] As shown in Fig. 44, in the diaper 3001A, a back side Ba and a front side Fr are determined, and a 47 G20801OO(JUN-048-PCT)_Eng. Spec_Final.doc back-side region S1, a crotch region S2, and a front-side region S3 are sequentially provided in the longitudinal direction L from the back side Ba to the front side Fr. [0279] As shown in Fig. 44, the pair of side flap portions 3010 are provided outside of the absorbent article body 3002 in the width direction on both sides of the absorbent article body 3002 in the width direction so as to extend in the longitudinal direction L of the absorbent article body 3002. [0280] The pair of back-side waist flap portions 3020 are provided in the back-side region S1 so as to protrude from the pair of side flap portions 3010 outward in the width direction of the absorbent article body 3002. [0281] The pair of front-side waist flap portions 3020 are provided in the front-side region S3 so as to protrude from the pair of side flap portions 3010 outward in the width direction of the absorbent article body 3002. [0282] The absorbent article body 3002 includes at least a liquid-permeable topsheet 3003, a liquid-impermeable backsheet 3004, and an absorber 3005 which is disposed between the topsheet 3003 and the backsheet 3004 and configured to absorb and retain liquid. [0283] The topsheet 3003 is made of hydrophilic nonwoven fabric, woven fabric, perforated hydrophobic nonwoven fabric, or the like. [0284] The backsheet 3004 is made of liquid-impermeable nonwoven fabric, liquid-impermeable film, a sheet obtained by bonding a hydrophilic nonwoven fabric and a liquid-impermeable film to each other, or the like. In this embodiment, the backsheet 3004 is formed by bonding a liquid-impermeable film 3004a and a liquid-impermeable nonwoven fabric 3004b to each other. [0285] The absorber 3005 is a laminate of a mixture of absorbent pulp and a highly absorbent polymer. [0286] The pair of side flap portions 3010 are made of the topsheet 3003 and the backsheet 3004 extended from the both sides of the absorbent article body 3002 in the width direction W. [0287] Elastic members 3012 extended are provided in the longitudinal direction L in each side flap portion 3012 at least in the crotch region S2. 48 G20801OO(JUN-048-PCT)_Eng. SpecFinal.doc [0288] As the elastic members 3012, four polyurethane-based elastic yams 470dtex stretched by a factor of 2.2 are used. [0289] The pair of back-side waist flap portions 3020 and the pair of front-side waist flap portions 3021 extend in the direction corresponding to the wearer's waistline direction (in the width direction W of the absorbent article body 302). [0290] Specifically, the pair of back-side waist flap portions 3020 are provided so as to protrude outward in the width direction W of the absorbent article body 3002 from the pair of side flap portions 3010 in the back-side region S1. The pair of front-side waist flap portions 3021 are provided so as to protrude outward in the width direction W of the absorbent article body 3002 from the pair of side flap portions 3010 in the front-side region S3. [0291] Herein, the back and front-side waist flap portions 3020 and 3021 are made of liquid-impermeable nonwoven fabric. [0292] Especially the pair of back-side waist flap portions 3020 are made of liquid-impermeable, heat-stretchable nonwoven fabric. In this embodiment, each of the pair of back-side waist flap portions 3020 is made of two sheet materials of 13 g/m 2 SMS which are bonded (see Fig. 46). [0293] At the top of each of the pair of back-side waist flap portions 3020, a locking member 3022 is provided. [0294] The locking member 3022 is locked with the front-side waist flap portion 3021. The locking member 3022 can be a hook-and-loop fastener locking with mechanical locking strength or adhesive tape locking with adhesive strength. [0295] When the locking member 3022 is a hook-and-loop fastener, each front-side waist flap portion 3021 is made of a sheet material having nonwoven fabric at least in the surface. [0296] In each of the pair of back-side waist flap portions 3020, a waistline stretched region 3023 is formed. [0297] Each waistline stretched region 3023 is provided in the vicinity of the corresponding side flap portion 3010, that is, at the base thereof. 49 G20801OO(JUN-048-PCT)_Eng. SpecFinal.doc [02981 Each waistline stretched region 3023 is formed so as to extend from the end on the front side Fr in the longitudinal direction L of the absorbent article body 3002. [0299] The ends of the waistline stretched regions 3023 on the back side Ba are short of the edges of the respective back-side waist flap portions 3020 on the back side Ba. Since the waistline stretched regions 3023 do not reach the edges of the respective back-side waist flap portions 3020 on the back side Ba, there are non-stretched regions F around the edges of the respective back-side waist flap portions 3020 on the back side Ba. [0300] In this embodiment, the length of the waistline stretched regions 3023 is set to 100 mm, and the length of the non-stretched regions F is set to 10 mm. [0301] The waistline stretched regions 3023 are reduced in basis weight by the stretching processing to have lower basis weight than the other region. [0302] As shown in Fig. 46, the waistline stretched region 3023 formed by the stretching processing has a structure in which dense portions (no referential numbers) stretched a small amount and low-dense portions (no referential numbers) stretched a large amount are alternately provided in the width direction W of the side flap portions 3010. [0303] The stretching processing is performed so that the dimension of each waistline stretched region 3023b expanded in the width direction W is larger at the end on the front side Fr than that at the end on the back side Ba. [0304] With such stretching processing, when the wearer wears the diaper 3001A, the back-side waist flap portions 3020 are extended a little on the back side Ba while being stretched much on the front side Fr. The diaper 1A can therefore fit to the crotch part of the wearer. [0305] The waistline stretched regions 3023 are specifically described with reference to Fig. 48. In Fig. 48, X indicates a dimension of each waistline stretched region 3023 in the width direction W before stretching (that is, an amount of stretch), and Y indicates a dimension of each waistline expanded region 3023 in the width direction W after stretching (that is, an amount of stretch). [0306] As described above, X and Y are set so that X<Y and the difference in dimension between X and Y is 50 G20801OO(JUN-048-PCT)_Eng. Spec_Final.doc preferably set to 0.5 to 10 cm. [0307] When the difference in dimension is less than 0.5 cm, the difference in length before and after stretching is small. For children whose circumferential lengths of waist and hip portions have a difference of 1 cm or more at least, the expanded lengths of the waistline stretched regions 23 cannot adjust for the difference between the waist and hip circumferential lengths. [0308] This makes a gap at the waist portion and results in a poor fit. Such a diaper will shift or leak excretion while being wom. [0309] On the other hand, when the difference in dimension between X and Y is more than 10 cm, for adults whose circumferential lengths of waist and hip portions have a difference of about 20 cm at maximum, the large difference in length between the stretched and not-stretched portions causes a gap at the hip portion stretched by stretching, thus leading to a poor fit. Such a diaper will shift or leak excretion while being wom. [0310] As shown in Fig. 49, the stretching machine 3030 includes a pair of stretching blade units 3031 which face each other and are meshed with each other [0311] Each stretching blade unit 3031 has a 2mm blade depth, a 1.25 pitch between a pair of blades, and 17 blades. [0312] The pair of back-side waist flap portions 3020 are heated to a temperature around the softening point and inserted between the stretching blade units 3031 for the stretching processing with the temperature of the stretching blade units 3031 set to 100C. [0313] By heating the stretching blade units 3031, the material of the pair of back-side waist flap portions 3020 comes close to the softening point and is more likely to expand, thus reducing the material damage due to the stretching processing. [0314] Moreover, if the material of the pair of back-side waist flap portions 3020 is not enough heated by the blades because of high processing speed, the pair of back-side waist flap portions 3020 may be previously heated before processing by the stretching blade units 3031. [0315] Stretching with such a stretching machine 3030 provides the dense portions stretched a small 51 G20801OO(JUN-048-PCT)_Eng. Spec_Final.doc amount and the low-dense portions stretched a large amount alternately in the width direction W in the pair of back-side waist flap portions 3020. [0316] As shown in Fig. 50, the diaper 3001A is worn by locking the locking portions 3022 of the pair of back-side waist flap portions 3020 to the surfaces of the pair of front-side waist flap portions 3021. [0317] When the wearer wears the diaper 3001A, the outer edge of each side flap portion 3010 comes into contact around the wearer's leg due to contraction of each of the elastic members 3012a to 3012d. [0318] In the pair of back-side waist flap portions 3020, the non-stretched regions F do not extend in the width direction W of the absorbent article body 3101, but the waistline stretched regions 3023 extend in the width direction W of the absorbent article body 3101. As described above, therefore, the dimensional difference between X and Y is caused. [0319] Accordingly, the diaper 3001 A can fit snugly to not only the waist but also the hips having a longer circumferential length than the waist. [0320] In the light of the points that the diaper 3001A can be made large enough to wrap around the hips and is not subject to the material defects, it is preferable that the pair of back-side waist flap portions 3020 in the waistline stretched region 3023 are stretched by a factor of 1.1 to 3.0 at the edges on the front side Fr. [0321] When the stretching ratio is less than 1.1, the waistline dimension of the pair of back-side waist flap portions 3021 is so small that the diaper 3001A cannot wrap around the hips enough. If the stretching rate is more than 3.0, the material could be badly damaged by stretching, thus causing material defects such as tears and holes. [0322] In the light of the fit to the hip portion and prevention of material defects, it is more preferable that the edges of the waist stretched regions 3023 on the front side Fr are stretched by a factor of 1.2 to 2.0. [0323] Moreover, each back-side waist flap portion 3020 can be provided in the direction corresponding to the wearer's waistline direction (in the width direction W of the absorbent article body 2), thus not increasing the material. Moreover, the manufacturing process cannot be complicated. [0324] In this embodiment, the pair of back-side waist flap portions 3020 does not expand except the 52 G2080100(JUN-048-PCT)_Eng. Spec_Final.doc waistline stretched regions 3023. Accordingly, the diaper 3001A can keep the same waistline dimension as that before the diaper 3001A is worn and will not shift while being wom. [0325] In this embodiment, the pair of back-side waist flap portions 3020 is provided with the portions other than the waistline stretched regions 3023 (non-stretched regions F) in the longitudinal direction L. This can prevent the pair of back-side waist flap portions 3021 from being reduced in strength as much as possible. [0326] In this embodiment, the waistline stretched regions 3023 are provided at the bases of the pairs of back-side waist flap portions 3020 (in the vicinity of the side flap portions 3010). Accordingly, the ends of the pair of back-side waist flap portions 3020 in the width direction W greatly move with respect to the inclination. It is therefore possible to obtain a desired displacement with the waistline stretched regions 3023 of small width. [0327] The dimension of the pair of back-side waist flap portions 3020 in the longitudinal direction L is determined by the wearer' shape and the entire diaper design and is therefore not particularly limited. However, it is preferable that the angle between the pair of back-side waist flap portions 3020 which is expanded and the virtual line of the diaper 3001 A in the width direction W is 0 to 30 degrees when the diaper 3001A is wom. [0328] If such an angle is less than 0 degree, the length around the waist is longer than that around the hips, resulting in a poor fit. The angle more than 30 degrees is not preferable because the tension by the back-side waist flap portions 3020 is hardly applied in the waistline direction, resulting in a poor fit. [0329] The pair of back-side waist flap portions 3020 and the pair of front-side waist flap portions 3021 are composed of members different from the pair of side flap portions 3010 in this embodiment but may be composed of a same member. Such a configuration can facilitate manufacturing the diaper 3001A. [0330] (Embodiment 4-2) Fig. 51 shows plan views of a diaper 3001 B according to Embodiment 4-2 of the present invention. Fig. 51(a) is a plan view of the diaper 3001 B not wom, and Fig. 51(b) is a plan view of the diaper 3001 B being wom. (0331] Compared to Embodiment 4-1, in the diaper 3001 B according to Embodiment 4-2, the waistline stretched regions 3023 are formed to both ends of each back-side waist flap portions 3020 in the longitudinal direction L. 53 G20801OO(JUN-048-PCT)_Eng. SpecFinal.doc [0332] The waistline stretched regions 3020 are formed over the entire length of the pair of back-side waist flap portions 3020. [0333] Moreover, in the waistline stretched regions 3023, the width dimension of the part subjected to the stretching processing is constant over the entire length of the back-side waist flap portions 3020, but the amount of stretch per unit length varies. [0334] The waistline stretched regions 3023 can be thus made wider on the front side Fr than on the back side Ba when being expanded (when the diaper is wom). [0335] As shown in Fig. 51(a), the width dimension of each waistline stretched region 3023 before the diaper is wom is indicated by a dimension H. As shown in Fig. 51 (b), the width dimension of each waistline stretched region 3023 when the diaper is being wom is a dimension I (H<l) on the back side Ba, and the width dimension of each waistline stretched region 3023 when the diaper is being wom is a dimension J (H<J and l<J) on the front side Fr. [0336] Such a relation in stretched amount ensures similar fit properties to Embodiment 4-1. [0337] The stretching processing at manufacturing of the diaper 3001 B of this embodiment can be carried out by changing the depth of the blades of the stretching blade units 3031 for the back and front sides Ba and Fr. [0338] The other configuration is the same as that of Embodiment 4-1. The redundant description is omitted, and the same components in the drawing are given the same reference numerals for clarification. [0339] In this embodiment, the width of the waistline stretched regions 3023 is constant in the longitudinal direction L. However, the ends of the waistline stretched regions 3023 are constraint to the portions not included the waistline stretched regions 302. Accordingly, the stretched amount is small at the end and increases away from the end. [0340] Accordingly, the waistline stretched regions 23 can efficiently form an inclined shape. [0341] (Embodiment 4-3) 54 G2080100(JUN-048-PCT)_Eng. Spec_Final.doc Fig. 52 shows plan views of a diaper 3001C according to Embodiment 4-3 of the present invention. Fig. 52(a) is a plan view of the diaper 3001 C which is not wom, and Fig. 52(b) is a plan view of the diaper 3001C in use. [0342] In the diaper 3001C according to Embodiment 4-3, similarly to Embodiment 4-2, the waistline stretched regions 3023 are formed over the entire length of the pair of back-side waist flap portions 3020. [0343] In this embodiment, in the waistline stretched regions 3023, the width dimension of the part subjected to the stretching processing varies over the entire length of the pair of back-side waist flap portions 3020. The width dimension of a waistline stretched sub-region 3023a on the front side Fr is set large while the width dimension of a waistline stretched sub-region 3023b on the back side Ba is set small. [0344] The width dimension of the waistline stretched sub-region 3023a on the front side Fr is larger than the width dimension of the waistline stretched sub-region 3023b on the back side Ba when the diaper 3001C is expanded (when the diaper 3001C is wom). [0345] As shown in Fig. 52(a), the width dimension of each waistline stretched region 3023 before the diaper is wom is indicated by a dimension H. As shown in Fig. 52(b), the width dimension of each waistline stretched sub-region 3023b when the diaper is wom is a dimension I (H<l) on the back side Ba, and the width dimension of each waistline stretched sub-region 3023a when the diaper is being wom is a dimension J (H<J and l<J) on the front side Fr. [0346] Such a relation in stretched amount ensures similar fit properties to Embodiment 4-1. [0347] The other configuration is the same as that of Embodiment 4-2. The redundant description is omitted, and the same components in the drawing are given the same reference numerals for clarification. [0348] In this embodiment, the pair of back-side waist flap portions 3020 in the width direction W are greatly displaced at top ends with respect to the inclination. It is therefore possible to obtain a desired displacement with the waistline stretched regions 3023 reduced in width dimensions and stretched amount as much as possible. [0349] (Embodiment 4-4) 55 G20801O0(JUN-048-PCT)_Eng. SpecFinal.doc Fig. 53 is a plan view of a diaper 3001 D according to Embodiment 4-4 of the present invention. [0350] The diaper 3001 D according to Embodiment 4-4 includes the pair of back-side waist flap portions 3020, which are beft-type, so as to extend in the direction orthogonal to the longitudinal direction L of the absorbent article body 3002 (in the width direction W). [0351] One of the back-side waist flap portions 3020 is provided with a locking portion 3022. [0352] The pairs of front-side waist flap portions 3021 are provided in the width direction W of the absorbent article body 3002 and are provided with locking members 3024 on the surfaces thereof, thus allowing the diaper 3001 D to be wom. [0353] In this embodiment, the waistline stretched regions 3023 are provided outside of each side flap portion 3010, thus improving the fit properties. [0354] The entire contents of Japanese Patent Application No. 2008-037921 filed on February 19, 2008 and PCT Patent Application PCT/JP2009/52646 filed on February 17, 2008 are incorporated herein by reference. INDUSTRIAL APPLICABILITY [0355] As described above, the absorbent article according to the present invention is useful as an absorbent article capable of fitting to a wearer, the absorbent article being made of less material and manufactured using facilitated processing at manufacturing. [0356] Moreover, the absorbent article according to the present invention can be prevented from exuding and leaking and moreover has good breathability. The absorbent article according to the present invention is an absorbent article which forms a so-called pocket under the wearer's crotch, the absorbent article being made of less material using facilitated processing at lower manufacturing cost accordingly. The present invention is usable also for absorbent articles including diapers. [0357] Furthermore, according to the absorbent article according to the present invention, the pair of waist flap portions can be extended in the direction corresponding to the wearer's waistline direction (in the width direction W of the absorbent article body) at manufacturing a product. On the other hand, with the waistline stretched regions, the pair of waist flap portions can be provided so as to incline toward the wearer's back side with respect to the wearer's waistline direction when the diaper is wom. 56 G2080100(JUN-048-PCT)_Eng. Spec_Final.doc [0358] According to the present invention, it is possible to provide an absorbent article snugly fitting to the body by a non-complicated manufacturing process without increasing the material. 57