SPECIFICATION Title of the Invention: LOCOMOTIVE CONTROL DEVICE, LOCOMOTIVE CONTROL SYSTEM AND STARTING CONTROL METHOD OF LOCOMOTIVE Technical Field [0001] The present invention relates to a locomotive control device to control-running of a locomotive which a plurality of vehicles are coupled to and pulls the vehicles, a locomotive control system where a plurality of locomotives pull vehicles, and a starting control method of a locomotive. Background Art [0002] When a plurality of vehicles are coupled, load is applied to couplers in case that the vehicles are pulled. In particular, in case that a formation becomes long as in a freight train, or in case that the number of power cars (locomotives) is small as compared with the total number of the vehicles, the load applied to the couplers becomes large, and thereby large vibration is applied to the vehicle to be pulled. Though there are many load factors applied to the couplers, one of the main factors is a shock load. [0003] This shock load is applied to the couplers when vehicles start and both couplers are engaged with each other, when a gap exists between the couplers before starting, or in the state that absorbers are allowed to expand, as shown in Fig. 12(a), (b). Since the shock load is generated mainly at 1 the time of starting, if starting speed is made low as much as possible, the shock load can be reduced. One of conventional technologies like this is the technology disclosed in Patent Document 1. In Patent Document 1, a special notch used for starting to generate a lower torque than power running at 1 notch is provided, and at the time of starting, an operator selects the special notch for starting and thereby a torque command can be moderately increased. Prior Art Document Patent Document [0004] Patent Document 1: Japanese Patent Application Publication No. Toku Kai 2004-49000 Summary of the Invention Problems to be solved by the Invention [0005] However, in the technology of Patent Document 1, since a train driver arbitrarily switches a notch position, when timing for making switchover from the special notch for starting to the power running at 1 notch is done too fast the speed may become high. As a result, there is a possibility that strong shock load is applied to the couplers. If timing for making switchover to the power running at 1 notch is delayed, it may take much time to start the vehicles. Means to solve the Problem [0006] The present invention is made in view of the above described circumstances, and its object is to provide a locomotive control device, a locomotive control system and a 2 starting control method of a locomotive, which can reduce shock load applied to couplers when starting without depending on a train driver's skills. [Means for Solving the Problem] [0007] To achieve the above-described object, a locomotive control device according to an embodiment of the present invention is characterized by comprising, a permissible speed memory unit configured to store a permissible speed of a locomotive so as to reduce shock at a moment when at least one pair of couplers is engaged, an engagement determining unit configured to determine whether or not the at least one pair of couplers is engaged, and a control unit configured to control the locomotive to run at a speed within the permissible speed till all of the at least one pair of couplers is engaged after starting, wherein the control unit automatically performs running control at the time of starting. [0008] If the embodiment is constructed like this, by arbitrarily setting the permissible speed, in case that the locomotive starts and pulls a plurality of the vehicles, while one pair of the couplers between the locomotive and the first succeeding vehicle is engaged to thereby cause shock load to be generated, the embodiment can control so that one pair of the couplers between the first and second succeeding vehicles is not engaged and thereby further shock load is not generated. 3 [0009] In addition, a locomotive control system according to an embodiment of the present invention is, in a system in which in case that locomotives, each including the above described locomotive control device, are separately arranged in a formation consisting of a plurality of vehicles characterized in that: a plurality of the locomotive control devices are constructed so that information can be transmitted to at least the locomotive control device positioned at its succeeding position, the locomotive control device firstly starts the starting control for the locomotive positioned at a leading side out of a plurality of locomotives at not more than the permissible speed, when it is determined that all of the at least one pair of couplers between the vehicles pulled by the started locomotive are engaged transmits a start permission command to the locomotive control device positioned at a succeeding side, and the locomotive control device which has received the start permission command starts the starting control for the relevant locomotive. [0010] If the embodiment is constructed like this, even in case that a plurality of the locomotives pull the vehicles, since after receiving that the starting control of the preceding locomotive have finished the succeeding locomotives sequentially start the starting control, it is avoided that the shock loads applied to one pair of the couplers are redundantly generated. [0011] In addition, a locomotive control system according 4 to an embodiment of the present invention is, in a system in which in case that locomotives, each including the above described locomotive control device, are separately arranged in a formation consisting of a plurality of vehicles characterized in that: the locomotive control device except the locomotive control device positioned at the most leading side out of a plurality of the locomotive control devices is provided with an immediately preceding coupler load detecting unit to detect a load applied to the couplers to couple the locomotive on which the locomotive control device itself is loaded with the immediately preceding vehicle, the locomotive control device of the locomotive positioned at the most leading side out of a plurality of locomotives firstly starts the starting control at not more than the permissible speed, and the locomotive control device loaded on the succeeding locomotive, when it is detected by its own immediately preceding coupler load detecting unit that the load has been applied to the couplers, starts the starting control at not more than the permissible speed. [0012] If the embodiment is constructed like this, even though means for transmitting information between a plurality of the locomotives is not provided, the locomotive control device loaded on the succeeding locomotive can properly start the starting control. 5 [0013] A starting control method of a locomotive according to an embodiment of the present invention is, in a starting control method of a locomotive to pull a plurality of vehicles, characterized in that, controlling the locomotive, till all of couplers to couple between the vehicles are engaged after starting, so that the locomotive runs at a speed within a permissible speed of the locomotive which is limited so as to reduce shock at a moment when the couplers is engaged. [0014] In addition, a starting control method of a locomotive according to an embodiment of the present invention is, in a starting control method of a plurality of locomotives in case that the locomotives are separately arranged in a formation consisting of a plurality of vehicles, characterized in that, starting the locomotive positioned at a leading side out of a plurality of the locomotives at not more than a permissible speed which is limited so as to reduce shock at a moment when two couplers are engaged, generating a start permission command to the succeeding locomotive when it is determined that all of the couplers between the vehicles pulled by the started locomotive are engaged, and starting the locomotive which has received the start permission command. [0015] In addition, a starting control method of a 6 locomotive according to an embodiment of the present invention is, in a starting control method of a plurality of locomotives in case that the locomotives are separately arranged in a formation consisting of a plurality of vehicles; characterized in that, starting the locomotive positioned at a leading side out of a plurality of the locomotives at not more than a permissible speed which is limited so as to reduce shock at a moment when a coupler is engaged, and starting succeeding locomotive at not more than the permissible speed when a load applied to the couplers to couple the locomotive itself and the immediately preceding vehicle is detected. Effect of the Invention [0016] According to a locomotive control device of the present invention, since a control unit automatically performs running control at the time of starting a train, the train can be started without depending on the operational skills of a driver while surely reducing shock load applied to one pair of couplers. [0017] According to a locomotive control system of the present invention, even in case that a plurality of locomotives pull vehicles, a train can be started while avoiding that the shock loads applied to one pair of couplers are redundantly generated. [0018] According to a starting control method of a 7 locomotive of the present invention, since running control is automatically performed at the time of starting a train, the train can be started without depending on the operational skills of a driver while surely reducing shock load applied to one pair of couplers. Brief Description of the Drawings [0019] [FIG. 1] A functional block diagram showing a construction of a locomotive control device according to a first embodiment. [FIG. 2] A view showing a train formation of vehicles pulled by the locomotive according to the first embodiment. [FIG. 3] A flow chart showing contents of starting control which the locomotive control device performs. [FIG. 4] A view showing states in which displacement amounts of the couplers change. [FIG. 5] A view showing states in which shock loads applied to the couplers are respectively generated. [FIG. 6] A functional block diagram showing a construction of a locomotive control device according to a second embodiment. [FIG. 7] A view showing a train formation of vehicles pulled by the locomotive according to the second embodiment. [FIG. 8] A view showing a train formation of vehicles pulled by locomotives according to a third embodiment. [FIG. 9] A sequence diagram showing a case in which the 8 locomotive control devices according to the third embodiment perform respective automatic starting controls in a coordinated manner. [FIG. 10] A view showing a train formation of vehicles pulled by locomotives according to a fourth embodiment. [FIG. 11] A sequence diagram showing a case in which the locomotive control devices according to the fourth embodiment perform respective automatic starting controls in a coordinated manner. [FIG. 12] A view to describe states in which couplers are engaged. Embodiments to practice the Invention [0020] Next, embodiments of the present invention will be described with reference to the drawings. [0021] (First Embodiment) Hereinafter, a first embodiment will be described with reference to Figs. 1 - 5. Fig. 1 is a functional block diagram showing a construction of a locomotive control device 2 arranged in a locomotive 1. The locomotive control device 2 includes a microcomputer and so on, and each of functional blocks shows a function which is put into practice with software. To the locomotive control device 2, a power running notch command and a brake command and so on are given from a principal control device 3 on a driver's platform, and in addition, speed information of the locomotive 1 is given from 9 a speed detecting unit 4. [0022] The locomotive control device 2 is provided with a position calculating unit 5 to calculate a position of the locomotive 1 based on a speed of the locomotive 1, a coupler engagement determining unit 6 to determine whether or not couplers are engaged based on the above-described position, a permissible speed memory unit 7 in which a predetermined permissible speed at the time of starting the locomotive 1 is stored, and a control command output unit (a control unit) 8 to output a command so as to control the running of the locomotive 1 based on the determination result of the engagement determining unit 6 and the above-described permissible speed to a drive control unit (including a drive circuit, such as an inverter) of a motor for running (an inductor motor, for example) not shown in the drawings, and so on. [0023] Fig. 2 shows a train formation of vehicles which are pulled by the locomotive 1. The locomotive 1 pulls three vehicles (freight cars, or passenger cars) 9A, 9B, 9C (the number N of the vehicles is 4) . The locomotive 1 and the vehicle 9A, the vehicle 9A and the vehicle 9B, and the vehicle 9B and the vehicle 9C are respectively coupled via couplers 10A, lOB, loC. [0024] Next, an operation of the present embodiment will 10 be described with reference to Figs. 3 - 6 in addition to Figs. 1 and 2. Fig. 3 is a flow chart showing starting control process executed by the locomotive control device 2. When a driver operates a power running notch not shown in the drawings in the state where the train stops, when the locomotive control device 2 detects a power running command outputted from the main control device 3 (usually, power running 1 notch), starts an automatic starting control. This automatic starting continues, till the driver makes a brake operation or the state that all coupling portions 10 have been engaged is determined, as described later. [0025] When the automatic starting control is initiated, to begin with, setting with respect to the determination of the engagement of the coupling portions 10 is performed as an initial setting (step Sl). In the present embodiment, the engagement of the coupling portion 10 is determined using a running distance of the locomotive 1 and a displacement amount of the coupling portion 10. Here, the displacement amount of the coupling portion 10 (hereinafter, referred to as a coupler displacement) is defined as an amount of change in the distance between two vehicles caused by components composing the coupling portion 10, such as a gap of the coupling portion 10 and expansion and compression of absorbers (not shown in the drawings). The value of the coupler displacement in the state in which the two vehicles to be coupled are in a most approximated state (a state in which the gap of the coupler 10 11 is maximum and the absorbers are most compressed) is determined as a minimum value of zero, and making this as a reference, when the two vehicles to be coupled are separated (the coupler 10 is engaged or the absorber is expanded), the value of the coupler displacement increases. The value of the coupler displacement becomes maximum in the state in which the coupling portion 10 is engaged and the absorbers are fully expanded. [0026] And, unless the driver performs stop operation, (step S2: NO), whether or not all the couplers 10 have been engaged is determined in a step S3. That is, assuming that a maximum value of the coupler displacement is Lc, the number of the vehicles is N, and a running distance of the locomotive 1 is Lr, it is determined that all the coupling portions 10 have been engaged in case that the following condition is satisfied. [0027] Lr > (N- 1) x Lc - (1) The running distance Lr is calculated by integrating the value of the speed outputted from the speed detecting unit 4 in the position calculating unit 5, but in addition, it may be calculated by obtaining the position information with the track antenna beacons or GPS (Global Positioning System), for example. [0028] During the automatic starting operation when continuously judged "NO" in the step S3, the control command output unit 8 controls the speed of the locomotive 1 so that the locomotive 1 runs at a high speed as much as possible in a 12 range not to exceed a permissible speed Vt stored in the permissible speed memory unit 7 (step S4) . The above-described permissible speed Vt is a value which has previously been set in the step S1, and is calculated in consideration of the overlap of shock loads in the coupler 10 in the present embodiment. [0029] Here, Fig 4 is referred to. In Fig. 4(a) (and Fig. 2), the couplers 10 in which the coupler displacements do not reach the maximum are shown by spring-shaped symbols, respectively. In addition, in Fig. 4 (b), the coupling portions 10 in the state in which the displacements of all the coupling portions 10 reach the maximum (that is, a state in which the conditional equation (1) comes into effect) are shown by linear symbols, respectively. [0030] A shock load is applied to the coupling portion 10A between the locomotive 10 and the vehicle 9A at the moment the coupling portion 10A itself is engaged, and in addition shock loads are applied to the coupling portion 10A in case that the coupling portion 10B between the vehicle 9A and the succeeding vehicles 9B, and the coupling portion 10C between the succeeding vehicles 9B, 9C are engaged, respectively. In this time, when the running speed of the vehicles 9 is slow, the shock loads at the moment the coupling portions 10 are respectively engaged are generated separately as shown in Fig. 5(a), but when the running speed becomes fast to some extent, the shock loads are generated at relatively same time as shown 13 in Fig. 5(b), and thereby large load is instantaneously applied to the coupling portion 10A. In order to prevent the overlap of the shock loads generated in this manner, before the succeeding vehicle 9 moves a distance corresponding to a gap (an initial displacement) held in the coupling portion 10 when the succeeding vehicle 9 stops, the shock load, generated by the running of the preceding vehicle 9, should be absorbed. [0031] Here, it is assumed that a time period Ts during which the shock load is applied to the coupling portion 10 is 10 msec, and an initial displacement LO of the coupling portion 10 is 5 mm, and the information like these is set in the step Si. In this case, if 1.8 km/h (= 5 mm / 10 msec) is determined as the permissible speed Vt, the shock loads which are sequentially generated in the coupling portions 10A, 10B, 10C, respectively, do not overlap. That is, at the time of transferring from the state shown in Fig. 4(a) to the state shown in Fig. 4(b), the train can be started so that the displacements of the coupling portions 10A, 10B, 10C intermittently reach the maximum displacements in sequence respectively. [0032] According to the present embodiment as described above, the control command output unit 8 of the locomotive control unit 2 automatically controls to make the locomotive 1 run at a speed within the permissible speed Vt till all the coupling portions 10 are engaged. In this case, since the permissible speed Vt is set to a quotient obtained by dividing 14 the initial displacement LO of the coupler 10 by the time period Ts during which the shock load is applied, in case that the locomotive 1 starts and thereby pulls a plurality of the vehicles 9, the locomotive control unit 2 can control such that the shock loads respectively generated with the engagement of the coupling portion 10 do not overlap. [0033] Accordingly, the train can be started while surely reducing the shock loads applied to the couplers 10, without depending on the operating skills of a train driver. For example, in such a case that the locomotive 1 pulls a sleeping car, since the vibration and noise applied to the sleeping car can be reduced at the time of starting, more comfortable boarding circumstance for passengers and crew members can be provided. In addition, the coupling determining unit 6 determines whether or not all the coupling portions 10 are engaged by the condition expression (1) which is based on the maximum displacement Lc in the coupling portion 10, the number N of the vehicles in the formation of the train and the running distance Lr of the locomotive 1. Accordingly, it can surely be avoided that the shock loads respectively generated in the coupling portions 10 overlap in terms of time. [0034] (Second Embodiment) Fig. 6 and Fig. 7 show a second embodiment, and the same symbols are given to the same portions as in the first embodiment and the description thereof is omitted, and hereinafter, different portions will be described. A 15 locomotive control device 12 installed on a locomotive 11 is provided with a rail track information memory unit 13, a formation information memory unit 14 and a maximum load calculating unit 15 in addition to the construction of the first embodiment. In addition, an engagement determining unit 16 and a control command output unit 17 are arranged in place of the engagement determining unit 6 and the control command output unit 8. And acceleration information which is calculated by an acceleration calculating unit 18 when the locomotive 11 is running and information of load generated in the coupling portion 10A which is detected by a coupling load detecting unit 19 are given to the locomotive control device 12. In addition, the acceleration calculating unit 18 may be an acceleration sensor to sense an acceleration of the locomotive control device 12. [0035] Next, an operation of the second embodiment will be described with reference to Fig. 7. The locomotive 11 in the second embodiment pulls a train with a comparatively long formation, such as N > 10, as shown in Fig. 7, and, in this case, a method for determining the engagement which the engagement determining unit 16 performs is different. The engagement determining unit 16 compares a load T applied to the coupling portion 10A of the locomotive 11 positioned at the fore front with a load (a maximum load) Ta in case that all the vehicles 9 are coupled to thereby perform the engagement determination. The maximum load Ta is calculated by 16 the maximum load calculating unit 15, but since it is the load at the time of starting, air resistance and curve resistance and so on are neglected, and the maximum load Ta is calculated by a following expression in consideration of a friction force between a wheel and a rail, an acceleration of a first vehicle, a slope and so on. [0036] Ta = NW [g (p + a + tan 0)] (2) Ta: a load applied to the coupling portion 10A in the state in which all the coupling portions 10 are engaged [N] N: the number of all vehicles W: an average mass of the vehicle 9 [kg] g: an acceleration of gravity [m/s 2 ] p: a coefficient of rolling friction of a wheel a: an acceleration of the locomotive 11 [m/s 2 ] 8: an average slope angle of second to last vehicles [rad] In addition, as e ' 0, it is assumed that cos e = 1, and sin e = tan e. Furthermore, there is also a case that the mass of the vehicle is expressed by the ton [t] and tan 9 is expressed by the per mill [r]. [0037] In the equation (2), the number of all vehicles N, the average mass of the vehicle W, the coefficient of rolling friction of the wheel p are stored and held in the formation information memory unit 14. The acceleration a of the locomotive 11 is measured and calculated by the acceleration 17 calculating unit 18, but as a matter of course, it may be calculated from the time change of the speed which the speed detecting unit 4 detects. And in case that T > Ta -- (3) it is determined that all the coupling portions 10 have been engaged. The load T applied to the coupling portion 10A of the leading locomotive 11 is measured by the coupler load detecting unit 19 (composed of a load sensor such as a strain gauge and a pressure sensor and so on, for example) installed at the coupling portion 10, but may be calculated from a torque value, a radius of the driving wheel and a travel resistance of the locomotive 11. [0038] In addition, the average slope angle 0 of second to last vehicles is calculated based on the slope information of the rail track stored in the rail track information memory unit 13 and the position of the locomotive 11 calculated by the position calculating unit 5. Proper values (average value, for example) are assumed for the distances between the vehicles 9, and thereby the slope state for the whole area of the formation can be grasped as shown in Fig. 7. tan 0 can be calculated by calculating a ratio of a vertical distance to a horizontal distance from the second vehicle 9 to the last vehicle 9, or by averaging the slopes at the respective vehicle positions. [0039] In such a case that the accuracy of the coupler load detecting unit 19 is not good, in order to prevent the 18 locomotive 11 from running while the automatic starting is not released, the engagement determination based on the position information may be performed supplementarily, in the same manner as in the first embodiment. [0040] According to the second embodiment as described above, when the maximum load calculating unit 15 calculates the maximum load Ta in case that all the vehicles 9 are coupled, and the coupler load detecting unit 19 detects the load T applied to the coupling portion 10A of the locomotive 11, the engagement determining unit 16 determines that all the coupling portions 10 are engaged in case that T > Ta. Accordingly, the engagement determination can be performed more surely, and the shock load can be alleviated when the train starts. [0041] (Third Embodiment) Fig. 8 and Fig. 9 show a third embodiment, and the portions different from the second embodiment will be described. The third embodiment shows a starting control which is performed in case that locomotives are arranged not only at the head but in the middle of a train formation as shown in Fig. 8(a). A leading locomotive 21 pulls three vehicles 24A 24C, a locomotive 22 which is following the vehicle 24C pulls two vehicles 25A and 25B, and a locomotive 23 which is following the vehicle 25B pulls three vehicles 26A - 26C, for example. [0042] In this case, the number of vehicles Ni - N3 in 19 local formations by the locomotives 21 - 23 are respectively shown as Ni = 4, N2 = 3, N3 = 4. The vehicles are respectively allocated to the locomotives to pull the relevant vehicles in this way, and locomotive control devices 27 - 29 which are respectively installed on the locomotives 21 - 23 make the locomotives start with fundamentally the same control as in case that the control devices themselves are at the head while cooperating with the control devices of the other locomotives. That is, each of the locomotive control devices 27 - 29 is constructed such that at least transmission of signals from the locomotive control device 27 to the locomotive control device 28 and transmission of signals from the locomotive control device 28 to the locomotive control device 29 are enabled through wire communication or wireless communication. Needless to say, each of the locomotive control devices 27 29 may be constructed so that bidirectional communications are enabled between them. [0043] Next, an operation of the third embodiment will be described with reference to also Fig. 9. Fig. 9 is a sequence diagram showing a processing in case that the locomotive control devices 27 - 29 which are respectively installed on the locomotives 21 - 23 perform automatic starting controls in a coordinated manner. When an automatic starting mode is started with a driver's starting operation, the locomotive control device 27 firstly controls the locomotive 21 to start. A method for starting the locomotive 21 is the same as in the 20 second embodiment except that the setting value of the number of the vehicles Ni is the number of vehicles which are taken care of by the locomotive 21. The locomotive control device 27 makes the locomotive 21 start while controlling so that the speed thereof becomes not more than the permissible speed, and when it is determined that all the coupling portions 10A - 10D of the vehicles 24A - 24C which are pulled by the locomotive 21 have been engaged as shown in Fig. B(b), the locomotive control device 27 transmits a start permission command to the locomotive control device 28 loaded on the locomotive 22 to thereby cause the locomotive 22 to start. [0044] A method for determining the engagement of the coupling portions 10 in the third embodiment is performed by the engagement determining unit 16 in the same manner as in the second embodiment. The locomotive 22 starts while its speed is kept not more than the permissible speed in the same manner as in the second embodiment, too. Concurrently with this start, the torque of the locomotive 21 is kept to be constant to thereby avoid that unnecessary loads are applied to the coupling portions 10A - 10D at the locomotive 21 side. [0045] And with respect to the locomotive 22, when it is determined that all the coupling portions 10 of the vehicles which are taken care of by it have been engaged, the locomotive control device 28 transmits a start permission command to the locomotive control device 29 installed on the locomotive 23 to thereby cause the locomotive 23 to start. 21 After the locomotive 23 starts, the locomotive 22 and the locomotive 21 run while keeping the torques thereof to be constant, respectively. When it is determined that the coupling portion 10 of the last vehicle 26C has been engaged, the locomotive control device 29 finishes the automatic starting control, and the control by a driver's notch operation is performed as in the usual running. [0046] According to the third embodiment as described above, the locomotive control devices 27 - 29 are each constructed so that communication is enabled, firstly the starting control is stated for the locomotive 21 located at the leading side at not more than the permissible speed, and when it is determined that all the couplers 10 between the vehicles 24A - 24c which are pulled by the locomotive 21 have been engaged, the locomotive control device 27 transmits the start permission command to the locomotive control device 28 located at the backward side, and the locomotive control device 28 which has received the start permission command starts the starting control of the locomotive 22. consequently, in case that a plurality of the locomotives are arranged in the vehicle formation, by making the locomotive control devices 27 - 29 which are respectively loaded on them cooperate, the shock loads applied to the coupling portions 10 can be reduced. [0047] (Fourth Embodiment) Fig. 10 and Fig. 11 show a fourth embodiment, and the 22 portions different from the third embodiment will be described. The vehicle formation of the fourth embodiment is the same as that of the third embodiment, but locomotive control devices 31 - 33 which are respectively installed on the locomotives 21 - 23 are different from those of the third embodiment and are not provided with communication function. In place of the communication function, the locomotive control devices 32, 33 which are installed on the locomotives 22, 23 are provided with immediately preceding coupler load detecting units 34, 35 which detect and calculate loads applied to the coupling portions 10 to couple the locomotives 22, 23 with their immediately preceding vehicles 24C, 25B, respectively. [0048] The immediately preceding load coupler detecting units 34, 35 are each a load sensor such as a strain gauge. That is, in case that the immediately preceding coupler load detecting unit 34 detects that load has been applied to the coupling portion 10D, it can be determined that all the coupling portions 10A - 10D which are preceding the locomotive 22 have been engaged. However, in case that it is necessary to grasp the control states of the locomotives 22, 23 at the locomotive 21 on which a driver rides, the communication function may be provided as in the third embodiment. [0049] Next, an operation of the fourth embodiment will be described with reference to also Fig. 11. Fig. 11 is a diagram corresponding to Fig. 9. When a starting operation is performed by a driver in the same manner as in the third 23 embodiment, the locomotive control device 31 firstly controls the preceding locomotive 21 to start, that is, makes it start while keeping its speed not more than the permissible speed in the same manner as in the first - third embodiments. And with respect to the other locomotives 22, 23, when it is detected with the immediately preceding coupler load detecting units 34, 35 that loads are applied to preceding coupling portions 1OF(2), 1OF(3), the locomotive control devices 32, 33 controls the locomotives 22, 23 to start, respectively. [0050] Here, a case that a load in the forward direction is applied means a time when a vehicle is pulled by the preceding vehicle or a time when a vehicle is pushed by the succeeding vehicle, for example. In addition to these cases, there are a case that a locomotive itself moves backward when brake is released in the state in which the locomotive stops at a rising slope and a case that a backward vehicle moves forward and pushes the locomotive in the state in which the locomotive stops at a falling slope. The starting control is started similarly in these cases. [0051] In addition, in the fourth embodiment, a maximum torque value is set which a motor for running can output at the time of starting in each of the locomotive control devices 31 - 33, and when each of the locomotive control devices 31 33 increases an output torque to the maximum torque value, then keeps the output torque to be constant. The load Ta is obtained in the case in which all the vehicles are coupled in 24 the same manner as in the second embodiment, and each of the maximum torque value is set by distributing the load Ta to each of the locomotives 21 - 23. The load Ta may be equally distributed, or the number of the vehicles which are taken care of by each of the locomotives is set as in the third embodiment, and the load Ta may be distributed depending on this proportion. And when the output torques of all the locomotives 21 - 23 reach the maximum torque values and then become in the states in which the output torques are kept to be constant, respectively, the automatic starting control is finished. [0052] According to the fourth embodiment as described above, in case that the locomotives 21 - 23 exist separately in the formation of a plurality of vehicles, firstly the locomotive control device 31 of the locomotive 21 which is located at the most leading side starts the starting control at not more than the permissible speed, and the locomotive control devices 32, 33 loaded on the succeeding locomotives 22, 23 start the starting controls at not more than the permissible speed when it is detected by the immediately preceding coupler load detecting units 34, 35 that the loads have been applied, respectively. Consequently, without performing communication among the locomotive control devices 31 - 33 as in the third embodiment, the train can be started so as to reduce the shock loads. [0053] In addition, after the locomotives 21 - 23 start, 25 since each of the locomotive control devices 31 - 33 controls so that when the output torque of the motor for running reaches the predetermined maximum torque value the output torque is kept to the maximum torque value, and since the maximum torque value of each of is set to a value obtained by dividing the maximum load Ta in case that all the coupling portions 10 have been engaged by the formation number of the vehicles which are pulled by each of the locomotives 21 - 23, the locomotive control devices 31 - 33 can make the respective locomotives 21 - 23 run while the output torques which are burdened to them are arbitrarily dispersed. [0054] The present invention is not limited to the embodiments which are described above or described in the drawings, but can be modified or expanded as described below. [0055] The formation number of the vehicles may be changed arbitrarily. The number of the locomotives in the third and fourth embodiments may be not less than four. [0056] In the case of determining the permissible speed Vt, the initial displacement LO and the applying time of the shock load Ts may be changed arbitrarily depending on an individual design. In addition, the permissible speed Vt is not limited to one which is determined by LO/Ts. [0057] The sharing control of the output torque in the fourth embodiment may be performed if necessary. In addition, the sharing control may be similarly applied to the third embodiment. 26 [0058] This application is based upon and claims the benefit of priority from Japanese patent Application No. 2009 109157 filed on April 28, 2009. These entire contents of the Japanese Patent Application are incorporated to this disclosure by reference. [0059] Since it is apparent that different embodiments can be widely made without departing from the spirit and scope of this invention, this invention is not limited to specific embodiments except those limited in the accompanying claims Industrial Applicability [0060] The present invention can be applied to a control for a locomotive. 27