JPH09294183A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent uneven illuminance of a light onto an original in the image reader. SOLUTION: A light guide member 7 to lead a light of a light source 10 provided to a side of the reader to an original is configured by arranging a plurality of light guide chips 8 side by side linearly in a main scanning direction of the reader (original read line direction). An adhered face 9 of each light guide chip 8 with respect to other light guide chip 8 is set so that the face 9 is intercepted to an optical axis of the incident light from the light source 10 (e.g. orthogonal or at an angle of 45 deg.). Part of the incident light from the light source 10 is reflected multiply in the inside of each light guide chip 8 and the reflected light is emitted in a line toward an original face from an emission face of the light guide member 7 with uniform illuminance independently of the distance from the light source 10. Or a refractive index of a collecting optical member of the light guide member at the original side is selected higher than that at the opposite side. Through the constitution above, it is prevented that the illuminance is higher toward the light source side in the main scanning direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading device for irradiating a document with light from a light source to read an image of the document, and more particularly to a light guide means for guiding the light from the light source to the document in the image reading device.

[0002]

2. Description of the Related Art FIG. 10 shows, for example, JP-A-6-17804.
It is a figure which shows schematic structure of the conventional color image reading apparatus shown by No. 8. In FIG. 10, the color image reading apparatus includes a light source 2 including an LED array, a mirror 5, a condenser lens 14, and an image sensor 3 including a CCD sensor. When the light source 2 is arranged on the document 1 as an image reading target and emits light, the light source light is applied to the document 1. The light reflected on the surface of the original is further reflected by the mirror 5, the optical path is changed, and the light is irradiated on the condenser lens 14. The condenser lens 14 condenses this light on the image sensor 3. Then, the sensor element of the image sensor 3 converts the emitted light into an electric signal, so that the image on the document is obtained as an electric signal. In this way, the color image reading apparatus sequentially irradiates the document 1 in the direction indicated by the arrow in the drawing (hereinafter, referred to as the sub-scanning direction) to convert the image of the document into an electric signal and reads the image.

The light source 2 is a line light source extending in a document reading line direction (hereinafter referred to as a main scanning direction) which is a depth direction in the drawing, and as shown in FIG. 11, a plurality of LED arrays 6a, 6b, 6c. .. are arranged side by side in the main scanning direction. Then, in order to obtain a color image, the light source 2 is a red (R), green (G), and blue (B) LED chip 6a to a light source corresponding to all three primary colors.
6c is manipulated in this order and arranged in parallel on a straight line.

As described above, in the conventional color image reading apparatus, the light source 2 uses the LED array, and the light sources for the three primary colors are composed of the LEDs, so that the arrangement space of the light source in the vicinity of the reading section of the apparatus is reduced. are doing. In addition, since the life of the LED is extremely longer than that of the tubular light source, the frequency of maintenance is reduced.

[0005]

However, in the conventional color image reading apparatus as described above, as shown in FIG.
As is clear from 1, the LED array of the light source 2 has each color,
That is, the R, G, and B LEDs are arranged side by side in this order, for example, and the LEDs of the same color are not continuously arranged. When reading a color image, the R, G, and B LEDs of the light source 2 are controlled to be turned on for each color in a predetermined order.

Therefore, in the conventional device, for example, L of R
When the ED was turned on, uneven illuminance on the document 1 occurred in the line longitudinal direction of the light source 2, that is, in the main scanning direction. The unevenness of the illuminance of the light source light on the original reduces the uniformity of the read image, resulting in the problem that only an apparatus having low image reading performance can be obtained.

The present invention has been made to solve the above-mentioned problems, and an object thereof is to provide an image reading apparatus capable of uniformly irradiating a document with light from a light source.

[0008]

In order to achieve the above object, an image reading apparatus of the present invention is an apparatus for irradiating a document with light and reading an image of the document with a linear sensor. It is characterized by having a different structure.

First, the image reading device is provided on one side of a document reading line direction which crosses the sub-scanning direction (document scanning direction) of the device, and a light source and a document along the main scanning direction (document reading line direction). The light guide means is disposed, and guides the light from the light source in the original reading line direction and linearly emits the light from the emission surface toward the original surface.

The light guide means is constructed by arranging a plurality of light guide chips in parallel in the main scanning direction. The light from the light source is partially reflected inside the light guide means (light guide chip) and emitted. Emit from the surface.

The light guide chip guides the light from the light source in the direction of the original reading line and supplies it to another adjacent light guide chip, and "multiple-reflects" the light in the light guide chip. Light is emitted from the emission surface of each light guide chip. In this case, the joint surface of each light guide chip is arranged at right angles to the incident optical axis from the light source.

In this way, each light guide chip transmits a part of the incident light, reflects the other at the joint surface, and emits the light toward the original. Therefore, the light from the light source provided "on one side in the main scanning direction", specifically, "on the side of the light guide means" irradiates the original with a substantially uniform light intensity at each position of the light guide means. To be done.

In a light guide means having another structure, a plurality of light guide chips having different chip lengths in the main scanning direction are arranged in parallel.

A light guide chip having a short chip length is provided on the far side of the light source. Specifically, for example,
The chip length of each light guide chip is set so as to be a geometric progression of the amount of reflected light on the joint surface of the light guide chip.

Further, it is also possible to adopt a configuration in which the reflectance at the joint surface of each light guide chip is set to be small on the light source side and large on the far side of the light source.

Further, in a different structure of the light guiding means,
The joint surface of each light guide chip is characterized in that the angle formed between the normal line and the incident optical axis differs between the light source side and the far side of the light source. The angle between the normal to the joint surface of the light guide chip and the incident optical axis is set to be larger on the light source side and smaller as it goes to the far side of the light source.

In the above structure, the light from the light source is partly reflected on the joint surface of each light guide chip and emitted from the emission surface, and the rest passes through the joint surface and is incident on the adjacent light guide chip. It By tilting the joint surface with respect to the incident optical axis as described above and adjusting the reflectance, etc., the amount of light reflected at the joint surface of each light guide chip can be adjusted, and the light is emitted from each light guide chip toward the original. The amount of light emitted can be made substantially uniform regardless of the distance from the light source. Furthermore, in such a configuration, the light utilization efficiency is better than in the case where the light guide chip bonding surfaces are arranged at right angles to the incident optical axis from the light source.

According to another aspect of the present invention, there is provided a light source provided on one side of the main scanning direction which crosses the sub-scanning direction of the apparatus, and a light guide means arranged on the original along the main scanning direction. Light guide means for guiding light from the light source in the main scanning direction and emitting light linearly from the emission surface toward the document surface. It consists of an optical member. The condensing optical member is characterized by having a large refractive index on the exit surface side and a small refractive index on the non-exit surface side.

By using such a condensing optical member, the light source is moved from the smaller refractive index to the larger refractive index at each position of the member, that is, from the non-emission surface side to the emission surface side of the member. The incident light from the light travels so as to draw an arc that expands in the traveling direction of the light. Therefore, light is efficiently emitted from the emission surface side of the condensing optical member toward the document. Also,
The light that has entered the portion with a small refractive index travels straight for a longer distance than the light that has entered the portion with a large refractive index, and is then bent to the one with the larger refractive index and emitted from the emission surface. Therefore, also in this configuration, light is emitted from each position of the light guide means with a substantially uniform light intensity.

In addition to the above-mentioned structure, the present invention can also adopt a structure in which a light quantity adjusting means is provided between the exit surface of the light guiding means and the original. In this case, a light blocking member can be used as the light amount adjusting means. If such a light amount adjusting means is provided on the emission surface and the light emission amount on the light source side is adjusted to be substantially equal to the light emission amount on the far side of the light source, the light emitted to the document on the light source side and on the far side of the light source is adjusted. It is easy to further improve the uniformity of strength.

In addition to the above-mentioned constitutions, a light reflecting film is provided on the surface of the light guide means excluding the emission surface. This light reflecting film prevents light from leaking out from the light guiding means and becoming ineffective light.

It is also possible to adopt a structure in which the area of the light reflecting film is changed between the light source side and the far side of the light source. in this case,
It is preferable that the area of the light reflecting film be increased toward the far side of the light source. If the area of the light reflection film is changed in this way, the amount of light emitted from the light guide in the distant side of the light source, which tends to decrease the amount of light emitted, can be increased. It is possible to further improve the uniformity of strength.

In the above-mentioned image reading apparatus, the light source used is any of the three color light sources of red, blue and green or the white light source. Further, the line-shaped sensor that reads the image of the document is a monochrome image sensor or a color image sensor. With the light source and the sensor having these configurations, the image reading device of the present invention can read a color image.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention (hereinafter, referred to as embodiments) will be described below with reference to the drawings. It should be noted that the same parts as those of the drawings already described are designated by the same reference numerals and the description thereof will be omitted.

Embodiment 1. 1 and 2 show the configuration of the image reading apparatus according to the first embodiment. FIG. 1 is a conceptual view of the image reading apparatus viewed from the sub-scanning direction with respect to the document, and FIG. 2 shows the apparatus of FIG. 1 in the main scanning direction.
That is, it is a conceptual diagram viewed from the main scanning direction. In the figure, a light source 10 is composed of, for example, three types of LED chips that respectively emit three colors of R, G, and B, and the light source 10 is arranged on one side in the main scanning direction. Also,
A rod-shaped light guide member 7 extending in the main scanning direction is arranged laterally of the light source 10, and light from the light source 10 is guided in the main scanning direction by the light guide member 7 and emitted from the light guide member 7. The light is emitted in a line from the surface and the original 1 is irradiated. In the figure,
The columnar condensing lens 4 is provided above the document 1 and collects the light emitted from the light guide member 7 and reflected by the document 1 on the linear image sensor 3. Further, the reflection plate 13 is arranged near the lower side surface of the condenser lens 4 in the sub-scanning direction along the longitudinal direction of the condenser lens 4, and more efficiently collects the light reflected by the document 1. Collected in 4.
When a single white light source is used as the light source 10, a color image can be read by using a color line sensor having a color filter as the line sensor.

The light guide member 7 comprises a plurality of light guide chips 8 arranged one-dimensionally in the main scanning direction. The overall shape of the light guide member 7 is, for example, a quadrangular prism, but may be a cylinder or the like. The light guide chip 8 is made of a transparent material such as glass or plastic, and each surface of the light guide chip 8 is a surface that is likely to undergo multiple reflection. In this embodiment,
The length of each light guide chip 8, that is, the length (optical path length) in the main scanning direction is constant, and the joint surface 9 is perpendicular to the incident optical axis of the light from the light source 10. Has been done. Further, the reflectance inside the light guide chip 8 is constant at each position inside the light guide member 7.

The light source light incident from the side surface of the light guide member 7 is
A part is multiply reflected inside each light guide chip 8, and a part is transmitted through the joint surface 9 and is incident on the adjacent light guide chip 8.
The light diffusely reflected by the joint surface 9 is further multiple-reflected and diffused in the light guide chip 8, and this is irradiated from the emission surface of each light guide chip 8 toward the document 1.

FIG. 3 shows the relationship between the intensity of light emitted from the light guide member 7 to the document surface and the distance of the light guide member 7 from the light source 10. As shown in FIG.
As described above, the emission intensity of light from the light guide member 7 is higher than that of the bonding surface 9 at the central portion of each light guide chip 8. Therefore,
By using the light guide member 7 of the present embodiment, the light source 10
The light can be uniformly emitted in the main scanning direction of the document 1 regardless of the distance from the.

Embodiment 2. The second embodiment is different from the first embodiment in the light guide chip constituting the light guide member 7, and the other configurations are the same.

FIG. 4 shows a schematic configuration of the image reading apparatus according to the second embodiment as viewed from the sub-scanning direction. FIG.
As shown in FIG. 3, in the second embodiment, the light guide chips 18 having different chip lengths, that is, different chip lengths in the main scanning direction, are arranged one-dimensionally in parallel to form the light guide member 7. There is. The chip length of the light guide chip 18 (optical path length in each light guide chip) is long on the light source 10 side and short on the far side of the light source 10. Further, the joint surface 19 with another light guide chip 18 is inclined (for example, 45 °) with respect to the incident optical axis, and the reflectance at the joint surface (or cut surface) 19 of each light guide chip 18 is It is set to a constant value.

When the light source 10 arranged on the side of the light guide member 7 having such a structure emits light and light is incident from the side surface of the light guide member 7, the incident light is incident on the joint surface 19 of the light guide chip 18. Are divided into transmitted light and reflected light, the transmitted light is incident on the adjacent light guide chips 18, and the reflected light is emitted from each light guide chip 18 toward the document 1.

Since the joint surface 19 of each light guide chip 18 is inclined with respect to the incident optical axis, the joint surface 1 is more than the amount of light that is multiply reflected in each light guide chip 18, diffused, and emitted.
The amount of light reflected by 9 and emitted from each light guide chip 18 toward the document 1 becomes larger.

Here, assuming that the amount of incident light is I, the reflectance at the joint surface 19 is r, and the number of joint surfaces of the light guide chip 18 is n, the amount of reflected light at the joint surface 19 of the nth chip is reflected. R is expressed as a function of the reflectance r at each joint surface 19 as in the following equation (1).

[0034]

## EQU00001 ## R = I.times. (1-r) ^(n-1) .times.r (1) Then, assuming that the chip length of each light guide chip 18 is l, this chip length l is, for example, The geometric progression of the reflected light amount R (l =
a, aR, aR ² , aR ³ , aR ⁴ ... A are constants. In the light guide member 7, as the distance from the light source 10 increases, the amount of incident light on the corresponding light guide chip 18 decreases. Therefore, the reflected light amount R
In the light guide member 7 decreases toward the far side of the light source 10. Therefore, as described above, the chip length 1 of the light guide chip 18 is shortened as n increases, so that the chip length 1 is proportional to the reflected light amount R, that is, the position of the bonding surface, that is, the original. The irradiation center position for 1 will be determined.

Therefore, the light that has entered the light guide member 7 having the structure shown in FIG. 4 from the light source 10 is emitted from each light guide chip 18 of the light guide member 7 with a uniform illuminance in the main scanning direction. Therefore, also in this embodiment, it is possible to uniformly irradiate the document with light in the main scanning direction without being affected by the distance from the light source.

Embodiment 3 FIG. The feature of the third embodiment is that the chip length of each light guide chip of the light guide member is fixed and the reflectance at the joint surface of each light guide chip is changed from the light source side to the far side of the light source. Is. Other configurations are similar to those of the above-described embodiment.

FIG. 5 shows the outline of the configuration of the third embodiment as viewed from the sub-scanning direction. As shown in FIG. 5, the light guide member 7 includes a plurality of light guide chips 28 arranged one-dimensionally in the main scanning direction. The chip length of each light guide chip 28 is constant, and the joint surface 29 of each light guide chip is set to have an inclination of, for example, 45 ° with respect to the incident optical axis.

Further, in this embodiment, a semi-reflective layer is provided on the joint surface 29 of each light guide chip 28,
The light incident on the light guide member 7 from the light source 10 is partially reflected by each semi-reflective layer and partially transmitted. Here, the reflectance r of the semi-reflective layer is set small on the light source side and set large as the distance from the light source 10 increases. On the other hand, the amount of light incident on each semi-reflective layer decreases as the distance from the light source 10 increases. Therefore, the light that has entered the light guide member 7 is reflected by the respective semi-reflective layers to approximately the same degree, and is irradiated onto the original 1. As described above, also with the configuration of the present embodiment, the illuminance on the light source side does not increase, and the illuminance on the document in the main scanning direction can be made uniform.

Embodiment 4 FIG. The feature of the fourth embodiment is that the inclination angle of the joint surface of each light guide chip of the light guide member with respect to the incident optical axis is changed according to the distance from the light source.

FIG. 6 shows an outline of the configuration of the fourth embodiment as viewed from the sub-scanning direction. As shown in FIG. 6, each chip length of the light guide chip 38 forming the light guide member 7 is constant, and the reflectance at the joint surface 39 of each light guide chip 38 is also constant. In the fourth embodiment, the angle between the normal line of the joint surface 39 of the light guide chip 38 and the optical axis of the incident light is increased on the light source side in order to make the irradiation intensity on the document uniform. It is made smaller on the far side. For this reason,
The bonding surface 39 on the light source side has a high rate of transmitting light, and the bonding surface 39 on the far side of the light source has a high rate of reflecting light. Therefore, the irradiation intensity of light on the original does not increase only on the light source side, and the illuminance on the original in the main scanning direction can be made uniform.

Embodiment 5. The feature of the fifth embodiment is that the light guide member formed of a plurality of light guide chips in the above embodiment is formed of a single converging optical material. FIG. 7 shows an outline of the configuration of the fifth embodiment as viewed from the sub-scanning direction. The light guide member 17 shown in FIG. 7 is composed of a converging optical member having different refractive indexes on the document side and the opposite side in the direction toward the document.

The converging optical member has a large refractive index on the original side and a small refractive index on the opposite side. The converging optical member is made of glass or the like, and the density of the material is changed to give the above-described distribution to the refractive index. Then, in the light converging optical member having such a refractive index distribution, light travels while being deflected to the one having a higher refractive index.

Therefore, in the fifth embodiment, as shown in FIG. 7, the light from the light source 10 incident on the light guide member 17 is deflected in the light guide member 7 toward the original side having a high refractive index, that is, Proceed in an arc toward the direction of travel.
Therefore, of the light that has entered inside from the side surface of the light guide member 17, the light that enters the high refractive index region of the light guide member 17, that is, the document side, is emitted toward the document on the light source side of the light guide member 17. To be done. On the other hand, the light incident on the low refractive index region of the light guide member 17, that is, on the opposite side of the document, travels straight in the light guide member 17 for a longer distance, is finally deflected to the document side, and is emitted toward the document. .

Therefore, the illuminance of the light on the original is prevented from becoming strong only on the light source side, and the original can be uniformly irradiated with the light in the main scanning direction as shown in FIG. Further, in the light guide member 17 of the fifth embodiment, the incident light is deflected to the original side and is emitted to the original 1, so that the light is diffused in the light guide member or the light leaks from the other surface of the light guide member. The light source light utilization efficiency is improved.

Embodiment 6. In the sixth embodiment, for example, in the same configuration as that of the first embodiment, the light amount adjusting means is provided on the exit surface of the light guide member 7 for the document. FIG. 8 is a schematic configuration diagram of the image reading apparatus of the sixth embodiment as viewed from the sub-scanning direction. As shown in FIG. 8, the bottom surface of the light guide member 7,
That is, the light shielding plate 11 is provided as a light amount adjusting means on the exit surface of the original. Further, the light blocking rate of the light blocking plate 11 is set to be large on the light source side and set to be small on the far side of the light source 10. With such a configuration, although the utilization efficiency of the light from the light source is somewhat lowered, it becomes possible to irradiate the original with light with a uniform illuminance in the main scanning direction. The light amount adjusting means of this embodiment can be adopted not only in the first embodiment but also in any of the second to fifth embodiments.

Embodiment 7 The feature of the seventh embodiment is that the light guide member 7 as shown in the first embodiment is provided with a reflection film on the surface other than the emission surface. FIG. 9 is a schematic view of the image reading device of the seventh embodiment as viewed from the sub-scanning direction. As shown in FIG. 9, an aluminum foil, for example, is provided as the reflective film 12 around the periphery of the light guide member 7 except the emission surface. The area of the light guide member 7 covered by the reflective film 12 is set to be small on the light source side and increase as the distance from the light source 10 increases. With this configuration, it is possible to increase the emitted light amount on the far side of the light source, which tends to lack the light amount. The reflective film 1 of the seventh embodiment
The configuration of 2 is also applicable to the other embodiments described above.

Further, in FIG. 9, the reflector 13 shown in the drawing according to another embodiment is not provided, but in order to improve the light-collecting property of the condenser lens 4 and the like, the reflector 13 is not provided. It is also possible to adopt a configuration in which.

[0048]

As described above, according to the present invention, the light guide member is provided between the light source and the document surface, and the light emitted from the light guide member is uniform regardless of the distance from the light source. Therefore, it is possible to reliably prevent the unevenness of the illuminance of light with respect to the original, and it is possible to read a more uniform image. In addition, since it is not necessary to make the light source directly face the original, the degree of freedom in layout of the image reading apparatus is improved.

[Brief description of drawings]

FIG. 1 is a diagram of an image reading apparatus according to a first embodiment of the present invention as viewed in a sub-scanning direction.

FIG. 2 is a conceptual view of the apparatus of FIG. 1 viewed from a main scanning direction.

FIG. 3 is a diagram showing a relationship between an irradiation intensity from a light guide member 7 in FIG. 1 and a distance from a light source.

FIG. 4 is a diagram of an image reading apparatus according to a second embodiment of the present invention as viewed in the sub-scanning direction.

FIG. 5 is a diagram of an image reading apparatus according to a third embodiment of the present invention as viewed in the sub-scanning direction.

FIG. 6 is a diagram of an image reading device according to a fourth embodiment of the present invention as viewed in the sub-scanning direction.

FIG. 7 is a diagram of an image reading device according to a fifth embodiment of the present invention when viewed in the sub-scanning direction.

FIG. 8 is a diagram of an image reading device according to a sixth embodiment of the present invention as viewed in the sub-scanning direction.

FIG. 9 is a diagram of an image reading device according to a seventh embodiment of the present invention as viewed in the sub-scanning direction.

FIG. 10 is a view of a conventional color image reading device as viewed from the main scanning direction.

11 is a diagram showing the configuration of the light source 2 of FIG.

[Explanation of symbols]

1 original, 3 image sensor, 4 condenser lens, 7,
17 light guide member, 8, 18, 28, 38 light guide chip,
9, 19, 29, 39 Bonding surface of light guide chip, 10 light source, 11 light shielding plate, 12 reflective film, 13 reflective plate.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Osamu Yajima 2-3-3 Marunouchi, Chiyoda-ku, Tokyo Sanryo Electric Co., Ltd.

Claims (16)

[Claims] 1. An image reading apparatus which irradiates a document with light and reads an image of the document by a linear sensor, comprising a light source provided on one side of a document reading line direction that crosses the document scanning direction of the device. A light guide unit arranged on the document along the document reading line direction, guiding light from the light source in the document reading line direction, and linearly directing light from a predetermined emission surface toward the document. A light guide means for emitting light to the light guide means, wherein the light guide means is configured by a plurality of light guide chips arranged in parallel in the document reading line direction, and inside the respective light guide chips, from the light source. The image reading device is characterized in that a part of the light is reflected and is emitted from the emission surface of each light guide chip. 2. Each of the light guide chips guides light from the light source in the original reading line direction and supplies the light to another adjacent light guide chip, and at the same time, the light is guided inside the light guide chip. The image reading device according to claim 1, wherein light is emitted from the emission surface of each light guide chip after partial reflection. 3. The image reading device according to claim 2, wherein a joining surface of each of the light guide chips and another light guide chip is arranged at a right angle to an incident optical axis from the light source. apparatus. 4. The light guide means is configured by arranging a plurality of light guide chips having different chip lengths in the document reading line direction in parallel, and a light guide chip having a shorter chip length is provided on a far side of the light source. The image reading device according to claim 1, wherein the image reading device is provided. 5. The light guide means is configured by arranging a plurality of light guide chips having different chip lengths in the original reading line direction in parallel, and the chip length of each light guide chip is equal to that of each light guide chip. It is set so as to be a geometric progression of the amount of reflected light on the joint surface with another light guide chip.
4. The image reading device described in any one of 4. 6. The reflectivity at the joint surface between each light guide chip and another light guide chip is small on the light source side and large on the far side of the light source. The image reading device according to one. 7. The joint surface of each light guide chip with another light guide chip is such that the angle formed by the normal line and the incident optical axis differs between the light source side and the far side of the light source. The image reading device according to claim 1, or any one of claims 3 to 6. 8. The image reading apparatus according to claim 7, wherein the angle between the normal line of the joint surface of the light guide chip and the incident optical axis becomes smaller toward the far side of the light source. 9. An image reading device which irradiates a document with light and reads an image of the document by a linear sensor, wherein a light source provided on one side of a document reading line direction crossing the document scanning direction of the device. A light guide unit arranged on the document along the document reading line direction, guiding light from the light source in the document reading line direction, and linearly directing light from a predetermined emission surface toward the document. And a light guide means for emitting light to the light guide means, wherein the light guide means is composed of a single condensing optical member, and the condensing optical member has a large refractive index on the emission surface side and does not emit light. An image reading device having a small refractive index on the surface side. 10. The image reading apparatus according to claim 1, further comprising a light amount adjusting unit provided between the light emitting surface of the light guiding unit and the document. 11. The image reading apparatus according to claim 10, wherein the light amount adjusting means is a light blocking member. 12. The image reading device according to claim 1, further comprising a light reflection film provided on a surface of the light guide unit other than the emission surface. 13. The image reading apparatus according to claim 12, wherein the area of the light reflecting film is changed between the light source side and the distant side of the light source. 14. The image reading apparatus according to claim 13, wherein the area of the light reflecting film increases as it goes farther from the light source. 15. The image reading apparatus according to claim 1, wherein the light source is one of three color light sources of red, blue and green or a white light source. 16. The image reading device, wherein the line-shaped sensor for reading the image of the document is a monochrome image sensor or a color image sensor.