Patent Publication Number: US-2022212705-A1

Title: Handcart

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. patent application Ser. No. 16/986,654 filed Aug. 6, 2020, which claims priority to Japanese Patent Application No. 2019-146884, filed on Aug. 8, 2019. 
     The entire disclosures of the prior applications are considered part of the disclosure of the accompanying continuation application, and are hereby incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The technique disclosed herein relates to a handcart. 
     BACKGROUND 
     Japanese Utility Model Registration No. 3210118 describes a handcart. This handcart includes a drive wheel, a prime mover configured to rotate the drive wheel, and a grip portion configured to be gripped by a user. 
     SUMMARY 
     When transferring work is performed with a handcart as described above, it is desirable, in order to ensure safety, to inform a person or a car coming from behind that the transferring work is in progress with the handcart. The disclosure herein provides a technique for informing a person or a car coming from behind that transferring work is in progress with a handcart. 
     A handcart disclosed herein may comprise a drive wheel; a prime mover configured to rotate the drive wheel; a grip portion configured to be gripped by a user; and a visibly noticeable portion that is clearly noticeable from behind the user when the user stands behind the handcart gripping the grip portion. 
     In the above configuration, the visually noticeable portion can be visually noticed from behind the user even when the user stands behind the handcart, gripping the grip portion. Thus, the configuration can inform a person or a car coming from behind that transferring work is in progress with the handcart. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a chassis unit  4  according to an embodiment, when seen from upper-front-right side, 
         FIG. 2  is an exploded perspective view of a handle unit  6  according to the embodiment, 
         FIG. 3  is a perspective view of a handle base  16  according to the embodiment, when seen from upper-front-right side, 
         FIG. 4  is a perspective view of the handle base  16  according to the embodiment, when seen from upper-rear-left side, 
         FIG. 5  is a perspective view of a right handle  18  according to the embodiment, when seen from upper-rear-left side, 
         FIG. 6  is a perspective view of a left handle  20  according to the embodiment, when seen from upper-rear-left side, 
         FIG. 7  is a perspective view of the chassis unit  4  with the right handle  18  and the left handle  20  fixed at a highest position, when seen from upper-front-right side, 
         FIG. 8  is a right side view of an internal structure of a switch box  40  according to the embodiment, 
         FIG. 9  is a right side view of the internal structure of the switch box  40  according to the embodiment, with a dead man&#39;s lever  42  pushed downward and an operation lever  72  pushed upward, 
         FIG. 10  is a rear view of the chassis unit  4  according to the embodiment, 
         FIG. 11  is a perspective view showing a positional relationship among the dead man&#39;s lever  42 , a first link member  84 , and a pipe  34  according to the embodiment, when they are seen from upper-front-right side, 
         FIG. 12  is a perspective view of a battery box  8  according to the embodiment, when seen from upper-rear-right side, 
         FIG. 13  is a perspective view of the battery box  8  according to the embodiment, when seen from upper-front-left side, 
         FIG. 14  is a vertical cross-sectional view of the battery box  8  according to the embodiment, 
         FIG. 15  is a perspective view of the battery box  8  according to the embodiment with a battery cover  106  opened, when seen from upper-rear-right side, 
         FIG. 16  is a vertical cross-sectional view of the battery box  8  according to the embodiment with the battery cover  106  opened, 
         FIG. 17  is a top view of a front wheel unit  12  according to the embodiment, 
         FIG. 18  is a perspective view of a brake equalizer  148  according to the embodiment, when seen from upper-rear-right side, 
         FIG. 19  is a top view of the brake equalizer  148  according to the embodiment, 
         FIG. 20  is a top view of the brake equalizer  148  according to the embodiment with a brake lever  49  pushed upward, 
         FIG. 21  is a horizontal cross-sectional view of a motor  150  and a gearbox  152  according to the embodiment, 
         FIG. 22  is a horizontal cross-sectional view of the motor  150  and the gearbox  152  according to the embodiment with a clutch lever  210  pulled up, 
         FIG. 23  is a perspective view of a dead man&#39;s brake  154  according to the embodiment, when seen from upper-front-right side, 
         FIG. 24  is a perspective view of a rear wheel unit  14  according to the embodiment, when seen from upper-front-right side, 
         FIG. 25  is a front view of the rear wheel unit  14  according to the embodiment, 
         FIG. 26  is a right side view of the rear wheel unit  14  according to the embodiment, 
         FIG. 27  is a vertical cross-sectional view of a center pin  230 , a top plate  232 , a bracket  234 , and a lock mechanism  240  of a right caster  226  according to the embodiment, 
         FIG. 28  is a vertical cross-sectional view of the bracket  234 , a wheel shaft  236 , and a right rear wheel  238  of the right caster  226  according to the embodiment, 
         FIG. 29  is a perspective view of a support plate  244  of the lock mechanism  240  according to the embodiment, when seen from upper-front-right side, 
         FIG. 30  is a perspective view of the right caster  226  according to the embodiment with a lock pin  242  retained by a first retainer portion  244   b,  when seen from upper-front-left side, 
         FIG. 31  is a perspective view of the right caster  226  according to the embodiment with the lock pin  242  retained by a second retainer portion  244   c,  when seen from upper-front-left side, 
         FIG. 32  is a top view of a right rear wheel  238  according to a variant with the right rear wheel  238  obliquely collided with a bump S, 
         FIG. 33  is a top view of the right rear wheel  238  according to the variant with the right rear wheel  238  facing the bump S, 
         FIG. 34  is a top view of a right rear wheel  238  according to the embodiment with the right rear wheel  238  obliquely collided with a bump S, 
         FIG. 35  is a top view of the right rear wheel  238  according to the embodiment with the right rear wheel  238  facing the bump S, 
         FIG. 36  is a perspective view of a coupling site of a chassis frame  10  and the rear wheel unit  14  according to the embodiment, when seen from upper-rear-right side, 
         FIG. 37  is a vertical cross-sectional view of the coupling site of the chassis frame  10  and the rear wheel unit  14  according to the embodiment, 
         FIG. 38  is a vertical cross-sectional view of the chassis frame  10  according to the embodiment with the rear wheel unit  14  pivoted, 
         FIG. 39  is a perspective view of the cart  2  according to the embodiment with a first container unit  300  attached to the chassis unit  4 , when seen from upper-front-right side, 
         FIG. 40  is a perspective view of the cart  2  according to the embodiment with the first container unit  300  attached to the chassis unit  4  and a container  302  lifted, when seen from upper-front-right side, 
         FIG. 41  is a perspective view of the first container unit  300  according to the embodiment with the container  302  lifted, when seen from lower-rear-left side, 
         FIG. 42  is a perspective view of a right guard retaining portion  328  according to the embodiment with a lower end of a support pipe  304   b  being in contact with a support plate  328   c,  when seen from upper-front right side, 
         FIG. 43  is a perspective view of the right guard retaining portion  328  according to the embodiment with a lower surface of a guard pipe  304   a  being in contact with an edge of the right guard retaining portion  328 , when seen from upper-front-right side, 
         FIG. 44  is a perspective view of the cart  2  according to the embodiment with the first container unit  300  attached to the chassis unit  4  and a right guard  304 , a left guard  306 , and a front guard  308  retained at a low position, when seen from upper-front-right side, 
         FIG. 45  is a perspective view of the cart  2  according to the embodiment with a second container unit  400  attached to the chassis unit  4 , when seen from upper-front-right side, 
         FIG. 46  is a perspective view of the cart  2  according to the embodiment with the second container unit  400  attached to the chassis unit  4  and a movable support base  408  tilted relative to a fixed support base  412 , when seen from upper-front-right side, 
         FIG. 47  is a perspective view of the cart  2  according to the embodiment with the second container unit  400  attached to the chassis unit  4 , the movable support base  408  tilted relative to the fixed support base  412 , and a bucket support base  404  tilted relative to the movable support base  408 , when seen from upper-front-right side, 
         FIG. 48  is a perspective view of the second container unit  400  according to the embodiment with the movable support base  408  tilted relative to the fixed support base  412  and the bucket support base  404  tilted relative to the movable support base  408 , when seen from upper-rear-left side, 
         FIG. 49  is a perspective view of the cart  2  according to the embodiment with a third container unit  500  attached to the chassis unit  4 , when seen from upper-front-right side, 
         FIG. 50  is a perspective view of the cart  2  according to the embodiment with the third container unit  500  attached to the chassis unit  4  and a movable support base  504  tilted relative to a fixed support base  508 , when seen from upper-front-right side, 
         FIG. 51  is a perspective view of the third container unit  500  according to the embodiment with the movable support base  504  tilted relative to the fixed support base  508 , when seen from upper-rear-left side, 
         FIG. 52  is a perspective view of the cart  2  according to the embodiment with a fourth container unit  600  attached to the chassis unit  4 , when seen from upper-front-right side, 
         FIG. 53  is a perspective view of the fourth container unit  600  according to the embodiment, when seen from lower-rear-right side, 
         FIG. 54  is a perspective view of the cart  2  according to the embodiment with a fifth container unit  700  attached to the chassis unit  4 , when seen from upper-front-right side, 
         FIG. 55  is a perspective view of the fifth container unit  700  according to the embodiment, when seen from lower-rear-left side, 
         FIG. 56  is a top view of a brake equalizer  148  according to a variant, 
         FIG. 57  is a top view of a brake equalizer  148  according to another variant, 
         FIG. 58  is a horizontal cross-sectional view of a motor  150  and a gearbox  152  according to a variant, 
         FIG. 59  is a horizontal cross-sectional view of the motor  150  and the gearbox  152  according to the variant with an inner cable  90   a  of a dead man&#39;s cable  90  pushed out relative to an outer cable  90   b,    
         FIG. 60  is a top view of a right rear wheel  238  according to the variant with the right rear wheel  238  pivoted such that a side surface thereof contacts a bump S, 
         FIG. 61  is a vertical cross-sectional view of a bracket  234 , a wheel shaft  236 , and a right rear wheel  238  of a right caster  226  according to a variant, 
         FIG. 62  is a perspective view showing a positional relationship among a dead man&#39;s lever  42 , a first link member  84 , and a second link member  86  according to a variant, when they are seen from upper-rear-left side, 
         FIG. 63  is a right side view of an internal structure of a switch box  40  according to the variant, and 
         FIG. 64  is a left side view of the internal structure of the switch box  40  according to the variant. 
     
    
    
     DETAILED DESCRIPTION 
     Representative, non-limiting examples of the present disclosure will now be described in further detail with reference to the attached drawings. This detailed description is merely intended to teach a person of skill in the art further details for practicing aspects of the present teachings and is not intended to limit the scope of the present disclosure. Furthermore, each of the additional features and teachings disclosed below may be utilized separately or in conjunction with other features and teachings to provide improved handcarts, as well as methods for using and manufacturing the same. 
     Moreover, combinations of features and steps disclosed in the following detailed description may not be necessary to practice the present disclosure in the broadest sense, and are instead taught merely to particularly describe representative examples of the present disclosure. 
     Furthermore, various features of the above-described and below-described representative examples, as well as the various independent and dependent claims, may be combined in ways that are not specifically and explicitly enumerated in order to provide additional useful embodiments of the present teachings. 
     All features disclosed in the description and/or the claims are intended to be disclosed separately and independently from each other for the purpose of original written disclosure, as well as for the purpose of restricting the claimed subject matter, independent of the compositions of the features in the embodiments and/or the claims. In addition, all value ranges or indications of groups of entities are intended to disclose every possible intermediate value or intermediate entity for the purpose of original written disclosure, as well as for the purpose of restricting the claimed subject matter. 
     In one or more embodiments, a handcart may comprise a drive wheel; a prime mover configured to rotate the drive wheel; a grip portion configured to be gripped by a user; and a visibly noticeable portion that is clearly noticeable from behind the user when the user stands behind the handcart, gripping the grip portion. 
     In this configuration, the visually noticeable portion can be visually noticed from behind the user even when the user stands behind the handcart, gripping the grip portion. Thus, the configuration can inform a person or a car coming from behind that transferring work is in progress with the handcart. 
     In one or more embodiments, the visibly noticeable portion may include at least one of a taillight configured to emit light and a reflector configured to receive and reflect light. 
     This configuration can surely inform a person or a car coming from behind that transferring work is in progress with the handcart, even when the handcart is used outdoor at night and/or in bad weather or the handcart is used indoor, for example, in a factory. 
     In one or more embodiments, the grip portion may include a grip extending in a front-rear direction. The visibly noticeable portion may be disposed forward of a rear end of the grip. 
     In this configuration, when an object collides with the handcart from behind it, the object collides with the rear end of the grip before reaching the visibly noticeable portion. Thus, damage to the visibly noticeable portion can be prevented. 
     In one or more embodiments, the handcart may further comprise a casing disposed near the grip and an operation member supported by the casing and configured to be operable by the user with the user gripping the grip. The prime mover may be configured to rotate the drive wheel when the operation member is operated by the user. 
     This configuration enables the user to perform an operation for driving the prime mover while the user grips the grip, thus it improves convenience for the user. 
     In one or more embodiments, the visibly noticeable portion may be disposed on a rear surface of the casing. 
     This configuration can simplify the configuration of the handcart as compared to a configuration in which the visibly noticeable portion is disposed separately from the casing which supports the operation member. 
     In one or more embodiments, the handcart may further comprise an alarm sound button supported by the casing and configured to be operable by the user with the user gripping the grip; and an alarm sound emitter configured to emit an alarm sound when the alarm sound button is operated by the user. 
     This configuration can inform a person or a car that is present in other directions than behind the handcart that transferring work is in progress with the handcart, by emitting the alarm sound from the alarm sound emitter. Further, the configuration enables the user to perform an operation for emitting the alarm sound from the alarm sound emitter while the user grips the grip, thus it can improve the user&#39;s convenience. 
     In one or more embodiments, the prime mover may include a motor. 
     This configuration can suppress vibrations transmitted to a load on the handcart as compared to a configuration in which an engine is used as the prime mover. 
     In one or more embodiments, the handcart may further comprise a battery mounting portion to which a battery is detachably attached. The motor may be driven by electric power from the battery. 
     This configuration enables the motor to be supplied with the electric power, without connecting the handcart with an external power supply via a power cord. 
     Embodiments 
     A cart  2  of the present embodiment is a hand cart. The cart  2  is configured by a chassis unit  4  shown in  FIG. 1  being removably attached to one of a first container unit  300  shown in  FIG. 39 , a second container unit  400  shown in  FIG. 45 , a third container unit  500  shown in  FIG. 49 , a fourth container unit  600  shown in  FIG. 52 , and a fifth container unit  700  shown in  FIG. 54 . In another embodiment, the cart  2  may be configured by the chassis unit  4  being unremovably attached to one of the first container unit  300 , the second container unit  400 , the third container unit  500 , the fourth container unit  600 , and the fifth container unit  700 . In the following description, one of the container units, among the first container unit  300 , the second container unit  400 , the third container unit  500 , the fourth container unit  600 , and the fifth container unit  700 , that is attached to the chassis unit  4  may be simply referred to as a container unit  800 . 
     (Chassis Unit  4 ) 
     As shown in  FIG. 1 , the chassis unit  4  includes a handle unit  6 , a battery box  8 , a chassis frame  10 , a front wheel unit  12 , and a rear wheel unit  14 . 
     (Handle Unit  6 ) As shown in  FIG. 2 , the handle unit  6  includes a handle base  16 , a right handle  18 , and a left handle  20 . The handle base  16  includes a base pipe  21 , a right channel  22 , a left channel  24 , a rectangular pipe  26 , a base plate  28 , a right attachment  30 , and a left attachment  32 . All of the base pipe  21 , the right channel  22 , the left channel  24 , the rectangular pipe  26 , the base plate  28 , the right attachment  30 , and the left attachment  32  are constituted of a steel material. A cross-sectional shape of the base pipe  21  is substantially circular. The base pipe  21  includes a central portion  21   a  extending in a right-left direction, a right support portion  21   b  bent downward from a right end of the central portion  21   a,  and a left support portion  21   c  bent downward from a left end of the central portion  21   a.  The right channel  22  includes a web  22   a  extending along a front-rear direction and an up-down direction, a front flange  22   b  bent leftward from a front end of the web  22   a,  and a rear flange  22   c  bent leftward from a rear end of the web  22   a.  The right support portion  21   b  of the base pipe  21  is welded to an upper portion of the right channel  22  on the left side thereof. The left channel  24  includes a web  24   a  extending along the front-rear direction and the up-down direction, a front flange  24   b  bent rightward from a front end of the web  24   a,  and a rear flange  24   c  bent rightward from a rear end of the web  24   a.  The left support portion  21   c  of the base pipe  21  is welded to an upper portion of the left channel  24  on the right side thereof. The rectangular pipe  26  extends in the right-left direction. A right end of the rectangular pipe  26  is welded to the vicinity of a center of the right channel  22  in the up-down direction on the left side thereof. A left end of the rectangular pipe  26  is welded to the vicinity of a center of the left channel  24  in the up-down direction on the right side thereof. The base plate  28  includes a wall  28   a  extending along the up-down direction and the right-left direction, and a floor  28   b  bent rearward from a lower end of the wall  28   a.  An upper end of the wall  28   a  is welded to a lower surface of the central portion  21   a  of the base pipe  21 . A lower surface of the floor  28   b  is welded to an upper surface of the rectangular pipe  26 . The right attachment  30  is welded to a lower end of the right channel  22 . The left attachment  32  is welded to a lower end of the left channel  24 . As shown in  FIG. 1 , the handle base  16  is fixed to the chassis frame  10  by the right attachment  30  being screwed to a frame plate  130  of the chassis frame  10  and the left attachment  32  being screwed to the frame plate  130  of the chassis frame  10 . 
     As shown in  FIG. 2 , the right handle  18  includes a pipe  34 , a channel  36 , a grip  38 , a switch box  40 , and a dead man&#39;s lever  42 . The pipe  34  and the channel  36  are both constituted of a steel material. The pipe  34  includes a support portion  34   a  extending in the up-down direction, and a handle portion  34   b  bent rearward from an upper end of the support portion  34   a.  The channel  36  includes a web  36   a  extending along the front-rear direction and the up-down direction, a front flange  36   b  bent rightward from a front end of the web  36   a,  and a rear flange  36   c  bent rightward from a rear end of the web  36   a.  The pipe  34  is welded to the channel  36  on the right side of the channel  36 . The grip  38 , the switch box  40  and the dead man&#39;s lever  42  are attached to the handle portion  34   b  of the pipe  34 . 
     The left handle  20  includes a pipe  44 , a channel  46 , a grip  48 , and a brake lever  49 . The pipe  44  and the channel  46  are both constituted of a steel material. The pipe  44  includes a support portion  44   a  extending in the up-down direction, and a handle portion  44   b  bent rearward from an upper end of the support portion  44   a.  The channel  46  includes a web  46   a  extending along the front-rear direction and the up-down direction, a front flange  46   b  bent leftward from a front end of the web  46   a,  and a rear flange  46   c  bent leftward from a rear end of the web  46   a.  The pipe  44  is welded to the channel  46  on the left side of the channel  46 . The grip  48  and the brake lever  49  are attached to the handle portion  44   b  of the pipe  44 . 
     The right handle  18  is fixed to the handle base  16  via grip bolts  50  and  52 . The left handle  20  is fixed to the handle base  16  via grip bolts  54  and  56 . The grip bolts  50 ,  52 ,  54 , and  56  respectively include heads  50   a,    52   a,    54   a,  and  56   a,  and shafts  50   b,    52   b,    54   b,  and  56   b.  As shown in  FIG. 3 , through holes  22   d  and  22   e  are formed in the web  22   a  of the right channel  22  of the handle base  16  such that the holes are arranged along the up-down direction. As shown in  FIG. 4 , nuts  58  and  60  are welded on a left surface of the web  22   a  of the right channel  22  at positions corresponding to the through holes  22   d  and  22   e.  Similarly, through holes  24   d  and  24   e  are f formed in the web  24   a  of the left channel  24  of the handle base  16  such that the through holes are arranged along the up-down direction. As shown in  FIG. 3 , nuts  62  and  64  are welded on a right surface of the web  24   a  of the left channel  24  at positions corresponding to the through holes  24   d  and  24   e.  As shown in  FIG. 5 , an elongated hole  36   d  extending in the up-down direction is formed in the web  36   a  of the channel  36  of the right handle  18 . As shown in  FIG. 6 , an elongated hole  46   d  extending in the up-down direction is formed in the web  46   a  of the channel  46  of the left handle  20 . 
     As shown in  FIG. 2 , to fix the right handle  18  to the handle base  16 , the shaft  50   b  of the grip bolt  50  is inserted through the elongated hole  36   d  of the right handle  18  and the through hole  22   d  of the handle base  16  and then is screwed into the nut  58 , and the shaft  52   b  of the grip bolt  52  is also inserted through the elongated hole  36   d  of the right handle  18  and the through hole  22   e  of the handle base  16  and then is screwed into the nut  60 . As a result, the channel  36  of the right handle  18  and the right channel  22  of the handle base  16  are held between the nuts  58 ,  60  and the heads  50   a,    52   a  of the grip bolts  50 ,  52 , with a left surface of the web  36   a  of the channel  36  of the right handle  18  being in contact with a right surface of the web  22   a  of the right channel  22  of the handle base  16 . The right handle  18  is fixed to the handle base  16  as above. In the following description, the grip bolts  50 ,  52  and the nuts  58 ,  60  may be collectively referred to as a right holder mechanism  51 . Further, the grip bolt  52  and the nut  60  may be referred to as a right rotation restricting mechanism  53 . The right rotation restricting mechanism  53  is configured to restrict rotation of the right handle  18  relative to the handle base  16  about the grip bolt  50  as a rotation axis. 
     Similarly, to fix the left handle  20  to the handle base  16 , the shaft  54   b  of the grip bolt  54  is inserted through the elongated hole  46   d  of the left handle  20  and the through hole  24   d  of the handle base  16  and then is screwed into the nut  62 , and the shaft  56   b  of the grip bolt  56  is also inserted through the elongated hole  46   d  of the left handle  20  and the through hole  24   e  of the handle base  16  and then is screwed into the nut  64 . As a result, the channel  46  of the left handle  20  and the left channel  24  of the handle base  16  are held between the nuts  62 ,  64  and the heads  54   a,    56   a  of the grip bolts  54  and  56 , with a right surface of the web  46   a  of the channel  46  of the left handle  20  being in contact with a left surface of the web  24   a  of the left channel  24  of the handle base  16 . The left handle  20  is fixed to the handle base  16  as above. In the following description, the grip bolts  54 ,  56  and the nuts  62 ,  64  may be collectively referred to as a left holder mechanism  55 . Further, the grip bolt  56  and the nut  64  may be referred to as a left rotation restricting mechanism  57 . The left rotation restricting mechanism  57  is configured to restrict rotation of the left handle  20  relative to the handle base  16  about the grip bolt  54  as a rotation axis. 
     The right handle  18  is configured to be movable in the up-down direction relative to the handle base  16 , with the grip bolts  50  and  52  loosened. Setting the right handle  18  to a desired position in the up-down direction relative to the handle base  16  and then tightening the grip bolts  50 ,  52  enables the right handle  18  to be fixed at the desired position relative to the handle base  16 . Similarly, the left handle  20  is configured to be movable relative to the handle base  16 , with the grip bolts  54 ,  56  loosened. Setting the left handle  20  to a desired position in the up-down direction relative to the handle base  16  and then tightening the grip bolts  54 ,  56  enables the left handle  20  to be fixed at the desired position relative to the handle base  16 . If the right handle  18  is integrated with the left handle  20  and a position of the integrated handle is adjusted in the up-down direction relative to the handle base  16 , a large amount of labor is required for the positional adjustment in the up-down direction relative to the handle base  16  because the weight of the integration of the right handle  18  and the left handle  20  is large. Contrary to this, in the cart  2  of the present embodiment, the right handle  18  and the left handle  20  are separate components, and their positions in the up-down direction relative to the handle base  16  can be adjusted individually. This arrangement can reduce an amount of labor required for the positional adjustment in the up-down direction relative to the handle base  16  because the individual weights of the right handle  18  and the left handle  20  are not so large. 
     As shown in  FIG. 3 , an elastic engagement piece  22   f  that protrudes rightward is disposed on the web  22   a  of the right channel  22  of the handle base  16 . As shown in  FIG. 4 , an elastic engagement piece  24   f  that protrudes leftward is disposed on the web  24   a  of the left channel  24  of the handle base  16 . A position of the elastic engagement piece  22   f  of the right channel  22  and a position of the elastic engagement piece  24   f  of the left channel  24  are substantially the same in the up-down direction. As shown in  FIG. 5 , a plurality of engagement holes  36   e  is formed in the web  36   a  of the channel  36  of the right handle  18 , corresponding to the elastic engagement piece  22   f  of the right channel  22 . The engagement holes  36   e  are arranged at predetermined intervals along the up-down direction. As shown in  FIG. 6 , a plurality of engagement holes  46   e  is formed in the web  46   a  of the channel  46  of the left handle  20 , corresponding to the elastic engagement piece  24   f  of the left channel  24 . The engagement holes  46   e  are arranged at predetermined intervals along the up-down direction. Positions of the engagement holes  36   e  of the right handle  18  and positions of the corresponding engagement holes  46   e  of the left handle  20  are substantially the same in the up-down direction. The right handle  18  can be fixed to the handle base  16 , with the elastic engagement piece  22   f  inserted in one of the engagement holes  36   e.  Similarly, the left handle  20  can be fixed to the handle base  16 , with the elastic engagement piece  24   f  inserted in one of the engagement holes  46   e.    
     Inserting the elastic engagement piece  22   f  to one of the engagement holes  36   e  and inserting the elastic engagement piece  24   f  to the corresponding one of the engagement holes  46   e  enables the right handle  18  and the left handle  20  to be fixed to the handle base  16  at the substantially same position in the up-down direction. For example, both the right handle  18  and the left handle  20  can be fixed at a lowest position relative to the handle base  16  as shown in  FIG. 1  by fixing the right handle  18  to the handle base  16  with the elastic engagement piece  22   f  inserted in the uppermost one of the engagement holes  36   e  and fixing the left handle  20  to the handle base  16  with the elastic engagement piece  24   f  inserted in the uppermost one of the engagement holes  46   e.  Alternatively, both the right handle  18  and the left handle  20  can be fixed at a highest position relative to the handle base  16  as shown in  FIG. 7  by fixing the right handle  18  to the handle base  16  with the elastic engagement piece  22   f  inserted in the lowermost one of the engagement holes  36   e  and fixing the left handle  20  to the handle base  16  with the elastic engagement piece  24   f  inserted in the lowermost one of the engagement holes  46   e.  Hereinafter, the elastic engagement piece  22   f  and the plurality of engagement holes  36   e  may be collectively referred to as a right positioning mechanism  23 , and the elastic engagement piece  24   f  and the plurality of engagement holes  46   e  may be collectively referred to as a left positioning mechanism  25 . 
     The right handle  18  can also be fixed to the handle base  16  by tightening the grip bolts  50  and  52  with the elastic engagement piece  22   f  not inserted in any of the engagement holes  36   e.  In this case, the elastic engagement piece  22   f  is pressed by the web  36   a  of the channel  36  and is maintained in a leftward elastically deformed state. Similarly, the left handle  20  can also be fixed to the handle base  16  by tightening the grip bolts  54  and  56  with the elastic engagement piece  24   f  not inserted in any of the engagement holes  46   e.  In this case, the elastic engagement piece  24   f  is pressed by the web  46   a  of the channel  46  and is maintained in a rightward elastically deformed state. 
     In another embodiment, the handle portion  34   b  of the right handle  18  may be bent rightward or leftward from the upper end of the support portion  34   a,  and the handle portion  44   b  of the left handle  20  may be bent rightward or leftward from the upper end of the support portion  44   a.  In yet another embodiment, the right handle  18  and the left handle  20  may be integrated, such as a U-shaped handle. 
     (Right Handle  18 ) 
     As shown in  FIG. 5 , in the right handle  18 , the switch box  40  is disposed frontward of the grip  38 . Further, the dead man&#39;s lever  42  is disposed above the grip  38 . 
     The switch box  40  includes a casing  66 , an operation panel  68 , an alarm sound button  70 , an operation lever  72 , and a taillight  74 . The casing  66  is a resin member. The operation panel  68  is disposed on an upper surface of the casing  66 . The operation panel  68  includes a main power button  68   a,  a main power indicator lamp  68   b,  a forward/backward mode switching button  68   c,  a forward mode indicator lamp  68   d,  a backward mode indicator lamp  68   e,  a speed switching button  68   f,  and a speed indicator  68   g.  The main power button  68   a  is a button for the user to switch on and off of a main power of the cart  2 . The main power indicator lamp  68   b  turns on when the main power of the cart  2  is turned on, and turns off when the main power of the cart  2  is turned off. The forward/backward mode switching button  68   c  is a button for the user to switch a forward mode and a backward mode of the cart  2 . In the forward mode, the cart  2  actuates a motor  150  (which will be described later, see  FIG. 1 ) to rotate a right front wheel  140  and a left front wheel  142  (which will be described later, see  FIG. 1 ) in a forward direction, while in the backward mode, the cart  2  actuates the motor  150  to rotate the right front wheel  140  and the left front wheel  142  in the reverse direction. The forward mode indicator lamp  68   d  turns on when the cart  2  operates in the forward mode, and turns off when the cart  2  operates in the backward mode. The backward mode indicator lamp  68   e  turns on when the cart  2  operates in the backward mode, and turns off when the cart  2  operates in the forward mode. The speed switching button  68   f  is a button for the user to switch a traveling speed of the cart  2 . In the cart  2  of the present embodiment, the traveling speed can be switched in multiple levels (e.g., in three levels). The cart  2  controls a rotational speed of the motor  150  when actuating the motor  150  in accordance with the traveling speed set by the speed switching button  68   f.  The speed indicator  68   g  changes the number of lit windows according to the traveling speed of the cart  2  set by the speed switching button  68   f.  As shown in  FIG. 8 , an operation board  76  is disposed inside the casing  66  and below the operation panel  68 . The operation board  76  includes switches (not shown) configured to detect user&#39;s operations on the main power button  68   a,  the forward/backward mode switching button  68   c,  and the speed switching button  68   f,  LEDs (not shown) configured to turn on/ turn off the main power indicator lamp  68   b,  the forward mode indicator lamp  68   d,  the backward mode indicator lamp  68   e,  and the speed indicator  68   g,  and the like. 
     As shown in  FIG. 5 , the alarm sound button  70  is disposed on a side surface of the casing  66  and leftward of the operation panel  68 . The alarm sound button  70  is a button for the user to activate a buzzer  124  (which will be described later, see  FIG. 13 ). When the user operates the alarm sound button  70 , the cart  2  activates the buzzer  124  to cause it to emit an alarming sound. If the cart  2  includes a speaker (not shown) other than the buzzer  124 , the cart  2  may be configured to output a predetermined music or sound from the speaker in response to the user&#39;s operation on the alarm sound button  70 . 
     The operation lever  72  is a resin member. As shown in  FIG. 8 , the operation lever  72  includes a support portion  72   a,  an operation piece  72   b,  and a detection piece  72   c.  The support portion  72   a,  the operation piece  72   b,  and the detection piece  72   c  are integrated with each other. The support portion  72   a  and the detection piece  72   c  are housed in the casing  66 . The operation piece  72   b  protrudes from the inside of the casing  66  to the outside thereof through an opening  66   a  formed in a rear surface of the casing  66 . The support portion  72   a  is pivotably supported with respect to the casing  66  around a pivot axis  72   d  extending in the right-left direction. An actuation switch  78  is housed in the casing  66  near the detection piece  72   c.  When the operation piece  72   b  is pushed upward by the user, the operation piece  72   b,  the support portion  72   a,  and the detection piece  72   c  are thereby integrally pivoted about the pivot axis  72   d,  and the actuation switch  78  is pressed by the detection piece  72   c  as shown in  FIG. 9 . The casing  66  also houses a compression spring (not shown) configured to apply a torque in a direction along which the operation piece  72   b  moves downward to the operation lever  72 . When the user releases the hand from the operation piece  72   b,  the operation piece  72   b,  the support portion  72   a,  and the detection piece  72   c  are integrally pivoted about the pivot axis  72   d  by the biasing force of the compression spring, and the detection piece  72   c  is separated from the actuation switch  78  as shown in  FIG. 8 . Around the operation piece  72   b,  the opening  66   a  of the casing  66  is covered by a bellows cover  80 . The bellows cover  80  prevents foreign matter from entering the inside of the casing  66  from the outside thereof through the opening  66   a.    
     The operation panel  68  is located on the upper surface of the casing  66 . The alarm sound button  70  is located on a side surface of the casing  66 . Further, the operation lever  72  is located rearward of the casing  66 . This arrangement enables the user to operate the operation panel  68 , the alarm sound button  70 , and the operation lever  72  by his/her fingers of the right hand while gripping the grip  38  with the right hand. 
     The taillight  74  is disposed on a rear surface of the casing  66  and below the operation lever  72 . The taillight  74  is turned on when a right headlight  156  and a left headlight  158  (which will be described later) are turned on, and is turned off when these lights are turned off. The taillight  74  is configured to emit light toward an area behind the cart  2  and serves as a visibly noticeable portion that can be clearly seen. As shown in  FIG. 8 , a taillight board  82  is disposed in the casing  66  and frontward of the taillight  74 . The taillight board  82  includes an LED (not shown) configured to turn on/off the taillight  74  and the like. The taillight  74  may be turned on/off by a surface-emitting LED, for example. For example, when the cart  2  collides with an object located behind while traveling backward, the grip  38  collides with the object before the object reaches the taillight  74  because the taillight  74  is located frontward of the grip  38 , thus the taillight  74  can be prevented from colliding with an object and getting damaged. 
     From a safety perspective for workers at night, the taillight  74  is desirable to be bright enough such that the lighting of the taillight  74  can be visually recognized at night from a point that is a distance of 100 m rearward apart from the taillight  74 . Further, the color of light emitted by the taillight  74  is desirably a color including red, specifically, orange, red, or the like. For example, if an LED is used, the lamp brightness that can be visually recognized at night from a point the distance of 100 m rearward apart may satisfy the standard for bike taillights specified in JISC9502 (in particular, the standard for brightness and/or color of beam of taillights). 
     The cart  2  may be configured to turn on the taillight  74  in conjunction with the activation of the cart  2 . The cart  2  may maintain the light of the taillight  74  constantly, and/or may cause it to blink. For example, the cart  2  may be configured to maintain the light of the taillight  74  constantly during normal operation and cause it to blink when an acceleration sensor (not shown) or the like detects deceleration of the cart  2 . Alternatively, the cart  2  may be configured to cause the light of the taillight  74  to blink during normal operation and maintain it constantly when an optical sensor (not shown) or the like detects that the environment gets dark. Further, the actuation of the motor  150  may be detected by a vibration sensor (not shown) or the like, and the cart  2  may be configured to maintain the light of the taillight  74  constantly when the environment gets dark and the motor  150  is actuated. Alternatively, the cart  2  may be configured to continue power supply to the taillight  74  while stopping power supply to the motor  150  and/or the container unit  800 , when a remaining charge of battery packs  112  (which will be described later, see  FIG. 14 ) is small. 
     The cart  2  may include a reflector (not shown) on the rear surface of the casing  66 , instead of the taillight  74 . The reflector emit light toward an area behind the cart  2  by receiving light and reflecting it, and serves as a visibly noticeable portion that can be clearly seen. The reflector may comprise a retroreflective material. When irradiated with light from a car headlight or the like at night, the reflector desirably provides reflected light that can be visually recognized from 100 m behind. The color of the light reflected by the reflector is desirably a color including red, specifically, an orange, red, or the like. Alternatively, a combination of the taillight  74  and the reflector may be used to further improve the visibility from behind. In this case, the taillight  74  may be integrated with the reflector. 
     As shown in  FIG. 10 , in a rear plan view of the chassis unit  4 , a distance D from a center of the chassis unit  4  in the right-left direction to a center of the taillight  74  in the right-left direction is 150 mm or more, preferably 200 mm or more, and is, for example, about 250 mm. For example, when the distance D is 150 mm or more, a distance between the right handle  18  and the left handle  20  is 300 mm or more, which is larger than a waist width of a standard adult. When the distance D is 200 mm or more, the distance between the right handle  18  and the left handle  20  is 400 mm or more, which is larger than a shoulder width of the standard adult. The distance D is selectable with the aforementioned standard waist width and shoulder width as its reference, considering the posture of a worker based on the shapes of the right handle  18  and the left handle  20 . With this configuration, even when the user is standing behind the cart  2  while gripping the right handle  18  and the left handle  20 , the taillight  74  is not blocked by the user&#39;s body and the taillight  74  can be visually recognized from behind the user. The center of the chassis unit  4  in the right-left direction may be any position corresponding to a center of the user&#39;s body in the right-left direction when the user is standing behind the cart  2  while gripping the right handle  18  and the left handle  20 . For example, the center of the chassis unit  4  in the right-left direction may be: a middle position between a center of a right front wheel  140  in the right-left direction and a center of a left front wheel  142  in the right-left direction; a middle position between a center of a right rear wheel  238  in the right-left direction and a center of a left rear wheel  258  in the right-left direction; a center position of the handle unit  6  in the right-left direction; or a middle position between a center of the grip  38  of the right handle  18  in the right-left direction and a center of the grip  48  of the left handle  20  in the right-left direction. The taillight  74  may be disposed at any position on the chassis unit  4  other than the switch box  40 , as long as the position is visually recognizable from behind the user when the user is standing behind the cart  2  while gripping the right handle  18  and the left handle  20 . For example, the taillight  74  may be disposed at the right channel  22  or the left channel  24  of the handle base  16 . Alternatively, the taillight  74  may be disposed at the channel  36  of the right handle  18  or on a rear end surface of the grip  38 . Alternatively, the taillight  74  may be disposed at the channel  46  of the left handle  20  or on a rear end surface of the grip  48 . Alternatively, the taillight  74  may be disposed near the right rear wheel  238  or near the left rear wheel  258  in a rear wheel frame  225  of the rear wheel unit  14  (which will be described later). Even if the taillight  74  is disposed at any of these positions, the light of the taillight  74  is desirably visually recognizable at night from 100 m behind. 
     As shown in  FIGS. 8 and 9 , the casing  66  further houses a first link member  84 , a second link member  86 , and a dead man&#39;s switch  88 . The first link member  84  is slidably supported by the casing  66  such that it can slide in a predetermined sliding direction (see arrows in  FIGS. 8 and 9 ). As shown in  FIG. 11 , the first link member  84  includes a support beam  84   a  that extends substantially linearly from its upper end to lower end, an auxiliary beam  84   b  that extends rightward from an intermediate part of the support beam  84   a  and then bends upward, and a pin  84   c  that extends rightward from a lower end of the support beam  84   a.  As shown in  FIGS. 8 and 9 , the support beam  84   a  is located leftward of the operation lever  72  and extends from an upper portion to a lower portion inside the casing  66 . The auxiliary beam  84   b  has a shape that does not interfere with the grip  38  and the operation lever  72  which are respectively located in an upper area and in a lower area within a movable range of the first link member  84 . The second link member  86  is pivotably supported by the casing  66  such that it can pivot about a pivot axis  86   a  extending in the right-left direction. An elongated hole  86   b  is formed at a rear end of the second link member  86 . The pin  84   c  of the first link member  84  is in the elongated hole  86   b  of the second link member  86 . When the first link member  84  slides in the sliding direction, the pin  84   c  presses a side wall of the elongated hole  86   b  while sliding along the side wall of the elongated hole  86   b,  which pivots the second link member  86  around the pivot axis  86   a.  The dead man&#39;s switch  88  is located to face a projection  86   c  disposed on the second link member  86 . When the second link member  86  is pivoted such that the rear end of the second link member  86  is moved upward, the projection  86   c  presses the dead man&#39;s switch  88 , whereas when the second link member  86  is pivoted such that the rear end of the second link member  86  is moved downward, the projection  86   c  is separated from the dead man&#39;s switch  88 . The second link member  86  is biased in a pivoting direction along which the rear end is moved upward by a torsion spring (not shown). A cable holder  86   d  is disposed at a front end of the second link member  86 . A dead man&#39;s cable  90  is inserted to a front lower portion of the casing  66 . The dead man&#39;s cable  90  includes an inner cable  90   a  and an outer cable  90   b  covering the periphery of the inner cable  90   a.  The outer cable  90   b  is supported by the casing  66 . The inner cable  90   a  is supported by the cable holder  86   d.    
     As shown in  FIG. 5 , the dead man&#39;s lever  42  has a shape that extends along an upper surface of the grip  38 . The dead man&#39;s lever  42  is a resin member. A rear end of the dead man&#39;s lever  42  is pivotably supported at a rear end of the grip  38  via a pivot axis  42   a  extending in the right-left direction. A front end of the dead man&#39;s lever  42  is slidably supported on an upper end of the first link member  84 . 
     When the user grips the grip  38 , the dead man&#39;s lever  42  is pushed downward by the user&#39;s palm. This moves the first link member  84  downward along the sliding direction and pivots the second link member  86  in a pivoting direction such that the rear end thereof is moved downward. As a result, as shown in  FIG. 9 , the inner cable  90   a  of the dead man&#39;s cable  90  is relatively pulled out from the outer cable  90   b.  Further, the projection  86   c  of the second link member  86  is separated from the dead man&#39;s switch  88 . When the user releases his/her hand from the grip  38  in this state, the biasing force of the torsion spring causes the second link member  86  to pivot such that the rear end is moved upward and the first link member  84  is thereby moved upward along the sliding direction. As a result, as shown in  FIG. 8 , the inner cable  90   a  of the dead man&#39;s cable  90  is relatively pushed into the outer cable  90   b.  Further, the projection  86   c  of the second link member  86  presses the dead man&#39;s switch  88 . Furthermore, the front end of the dead man&#39;s lever  42  is pushed upward. 
     The first link member  84  and the second link member  86  may be configured as shown in  FIG. 62 . In the configuration shown in  FIG. 62 , the pin  84   c  of the first link member  84  extends leftward from the lower end of the support beam  84   a.  Further, the first link member  84  includes a roller  84   d  that is rotatably supported by the pin  84   c  and a block  84   e  that protrudes rightward from the lower end of the support beam  84   a.  In the configuration shown in  FIG. 62 , the elongated hole  86   b  and the projection  86   c  are not disposed on the second link member  86 . In the vicinity of the rear end of the second link member  86 , the roller  84   d  of the first link member  84  is in contact with an upper surface of the second link member  86 . 
     In a configuration using the first link member  84  and the second link member  86  shown in  FIG. 62 , the internal space of the casing  66  is partitioned by an inner wall  66   b  into a left space and a right space as shown in  FIGS. 63 and 64 . An elongated hole  66   c  is formed in the inner wall  66   b.  A longitudinal direction of the elongated hole  66   c  is along the sliding direction of the first link member  84 . As shown in  FIG. 63 , the support beam  84   a  and the block  84   e  of the first link member  84  and the dead man&#39;s switch  88  are disposed in the right space which is located on the right side relative to the inner wall  66   b.  The pin  84   c  of the first link member  84  passes through the elongated hole  66   c.  As shown in  FIG. 64 , the roller  84   d  of the first link member  84 , the second link member  86 , and the dead man&#39;s cable  90  are disposed in the left space located on the left side relative to the inner wall  66   b.    
     In the configuration shown in  FIGS. 62 to 64 , when the dead man&#39;s lever  42  is pushed downward by the user, the first link member  84  is moved downward along the sliding direction and the roller  84   d  presses the upper surface of the second link member  86  near the rear end thereof while rolling thereon. This pivots the second link member  86  about the pivot axis  86   a  and moves the front end of the second link member  86  upward, as a result of which the inner cable  90   a  of the dead man&#39;s cable  90  is relatively pulled out from the outer cable  90   b.  Further, when the first link member  84  is moved downward along the sliding direction, the block  84   e  of the first link member  84  presses the dead man&#39;s switch  88 . When the user releases his/her hand from the dead man&#39;s lever  42  in this state, the biasing force of the torsion spring (not shown) causes the second link member  86  to pivot in the pivoting direction such that its front end is moved downward and its rear end is moved upward. As a result, the inner cable  90   a  of the dead man&#39;s cable  90  is relatively pushed into the outer cable  90   b.  Further, when the roller  84   d  is pushed upward by the upper surface of the second link member  86 , the first link member  84  is moved upward along the sliding direction and the block  84   e  of the first link member  84  is separated from the dead man&#39;s switch  88 . Furthermore, the front end of the dead man&#39;s lever  42  is pushed upward. 
     A signal cable  92  is inserted into the front lower portion of the casing  66 . Wires extending from the operation board  76 , the alarm sound button  70 , the actuation switch  78 , the taillight board  82 , and the dead man&#39;s switch  88  in the casing  66  are drawn out of the casing  66  through the signal cable  92 . 
     (Left Handle  20 ) 
     As shown in  FIG. 6 , in the left handle  20 , a brake cable  94  is connected to the brake lever  49 . The brake cable  94  includes an inner cable  94   a  and an outer cable  94   b  covering the periphery of the inner cable  94   a.  The brake lever  49  is pushed downward by a biasing force of a torsion spring (not shown). When the user pushes the brake lever  49  upward, the inner cable  94   a  of the brake cable  94  is relatively pulled out from the outer cable  94   b.  When the user releases his/her hand from the brake lever  49 , the brake lever  49  is pushed downward by the biasing force of the torsion spring and the inner cable  94   a  of the brake cable  94  is relatively pushed into the outer cable  94   b.    
     (Battery Box  8 ) 
     As shown in  FIGS. 12 and 13 , the battery box  8  includes a casing  100 , a top cover  102 , a front cover  104 , and a battery cover  106 . The casing  100 , the top cover  102 , the front cover  104 , and the battery cover  106  are constituted of resin. The casing  100  has a box shape. The top cover  102  is attached to an upper surface of the casing  100 . The top cover  102  has a substantially flat plate shape and is inclined downward from the front toward rear. The front cover  104  is attached to a front surface of the casing  100 . The front cover  104  has a substantially flat plate shape and is substantially perpendicular to the front-rear direction. The battery box  8  is fixed to the handle unit  6  by screwing the front cover  104  to the wall  28   a  (see  FIG. 2 ) of the base plate  28  with the battery box  8  placed on the floor  28   b  (see  FIG. 2 ) of the base plate  28  of the handle unit  6 . 
     As shown in  FIG. 14 , a control board  108  is housed in the casing  100 . Further, a plurality of battery mounting portions  110  is disposed on a rear surface of the casing  100 . A plurality of battery packs  112  is detachably attached to the plurality of battery mounting portions  110 . The battery packs  112  each include, for example, a secondary battery cell such as a lithium ion battery cell (not shown) and are configured to be charged by a charger (not shown). Each of the battery packs  112  has, for example, a rated voltage of 18V and a rated capacity of 6.0 Ah. The battery packs  112  can be also used in an electric device other than the cart  2 , for example, in an electric power tool such as electric driver, or an electric working machine such as electric mower. As shown in  FIG. 15 , in the cart  2  of the present embodiment, the plurality of battery packs  112  (e.g., four battery packs  112 ) is grouped into first-group battery packs  112   a  (e.g., two battery packs on the left) and second-group battery packs  112   b  (e.g., two battery packs on the right). The cart  2  of the present embodiment is switchable between a state in which the cart  2  uses the first-group battery packs  112   a  connected in series as the power source and a state in which the cart  2  uses the second-group battery packs  112   b  connected in series as the power source. 
     As shown in  FIG. 12 , the battery cover  106  is attached to the casing  100  via a hinge  106   a  disposed at an upper end of the battery cover  106 . The battery cover  106  is pivotable relative to the casing  100  about a pivot axis  106   b  extending in the right-left direction. As shown in  FIGS. 12 and 13 , the battery cover  106  includes an upper inclined surface  106   c  that is inclined downward from the front to rear, a lower inclined surface  106   d  that is continuous from the upper inclined surface  106   c  and is inclined downward from the rear to front, a bottom surface  106   e  that is continuous from the lower inclined surface  106   d  and is substantially perpendicular to the up-down direction, a right side surface  106   f  that connects right ends of the upper inclined surface  106   c,  the lower inclined surface  106   d,  and the bottom surface  106   e,  and a left side surface  106   g  that connects left ends of the upper inclined surface  106   c,  the lower inclined surface  106   d,  and the bottom surface  106   e.  A recessed surface  106   h  which is recessed toward the front is disposed at an upper portion of the upper inclined surface  106   c,  and the hinge  106   a  is disposed on the recessed surface  106   h.  As shown in  FIG. 14 , the battery cover  106  covers the periphery of the plurality of battery packs  112  attached to the battery mounting portions  110  when the battery cover  106  is closed with respect to the casing  100 . In this state, an upper surface of the top cover  102  and an upper surface of the battery cover  106  are inclined relative to a horizontal surface. Thus, even when water adheres to the upper surface of the top cover  102  and/or the upper surface of the battery cover  106 , the water travels along the upper surface of the top cover  102  and/or the upper surface of the battery cover  106  and then drops downward from the battery box  8 . 
     As shown in  FIGS. 15 and 16 , when the battery cover  106  is open with respect to the casing  100 , the battery packs  112  can be removed or attached with respect to the battery mounting portions  110  by being slid in a predetermined sliding direction (see an arrow in  FIG. 16 ). When the battery cover  106  is open with respect to the casing  100 , the battery cover  106  is located at a position that does not interfere with the sliding of the battery packs  112 . Thus, the opened battery cover  106  does not interfere with the attachment or detachment of the battery packs  112 . 
     As shown in  FIGS. 14 and 16 , the pivot axis  106   b  of the battery cover  106  is located below the top cover  102 , and a rear end of the top cover  102  extends rearward beyond the pivot axis  106   b.  Thus, as shown in  FIG. 14 , in a top view of the battery box  8  with the battery cover  106  closed with respect to the casing  100 , the battery cover  106  and the top cover  102  partially overlap with each other. Further, as shown in  FIG. 16 , in the top view of the battery box  8  with the battery cover  106  opened with respect to the casing  100 , the battery cover  106  and the top cover  102  partially overlap with each other. Even though water adheres to an outer surface of the top cover  102  and/or an outer surface of the battery cover  106 , such a configuration can prevent the water from dripping onto the battery packs  112  attached to the battery mounting portions  110 . An eaves  102   a  overhanging the hinge  106   a  is disposed at a position correspond to the hinge  106   a  in the rear end of the top cover  102 . This can suppress water droplets from adhering to the hinge  106   a  and affecting the pivoting of the battery cover  106 . 
     As shown in  FIGS. 15 and 16 , a water tray  110   b  surrounded by a side wall  110   a  is disposed on upper surfaces of the battery mounting portions  110 . Thus, even if water drops onto the upper surfaces of the battery mounting portions  110 , the water is suppressed from reaching the battery packs  112  attached to the battery mounting portions  110 . 
     As shown in  FIG. 15 , a sealing member  114  may be attached to the rear surface of the casing  100 . The sealing member  114  is, for example, a rubber  0 -ring and is disposed around the plurality of battery mounting portions  110 . A rib  116  is disposed on an inner surface of the battery cover  106 , corresponding to the sealing member  114 . When the battery cover  106  is closed with respect to the casing  100 , the rib  116  contacts and presses the sealing member  114 . This prevents water from entering the inside of the battery cover  106  while the battery cover  106  is closed with respect to the casing  100 . 
     The battery cover  106  is biased by a torsion spring (not shown) in a direction that closes the battery cover  106  with respect to the casing  100 . In the cart  2 , the gravity on the battery cover  106  acts as a force in the direction that closes the battery cover  106  with respect to the casing  100 . A latch member  118 , which is configured to be operable by the user, is disposed on the battery cover  106 . The latch member  118  can keep the battery cover  106  closed by engaging with a latch receiver  100   a  disposed in a lower portion of the casing  100  when the battery cover  106  is closed. 
     As shown in  FIG. 12 , an operation panel  120  is disposed on the top cover  102 . The operation panel  120  includes a battery remaining charge indicator  120   a,  a power supply switching knob  120   b,  a lighting button  120   c,  a display switching button  120   d,  and a container operation switch  120   e.  The battery remaining charge indicator  120   a  corresponds to the plurality of battery packs  112  attached to the plurality of battery mounting portions  110  and changes the number of lighted windows according to battery remaining charge of the plurality of battery packs  112  attached to the plurality of battery mounting portions  110 . The power supply switching knob  120   b  is a knob for the user to switch the power supply of the cart  2  between the first-group battery packs  112   a  and the second-group battery packs  112   b.  The lighting button  120   c  is a button for the user to switch on/off of a right headlight  156  and a left headlight  158 , which will be described later. The display switching button  120   d  is a button for the user to switch on/off of the display of battery remaining charge by the battery remaining charge indicator  120   a.  The container operation switch  120   e  is, for example, a momentary rocker switch and is a switch for accepting user&#39;s operations to the container unit  800 . As shown in  FIGS. 14 and 16 , an operation board (not shown) and a power supply switching switch  122  are housed in the casing  100  below the operation panel  120 . The operation board includes an LED (not shown) for lighting/un-lighting the battery remaining charge indicator  120   a  and switches (not shown) for detecting user&#39;s operations to the lighting button  120   c  and the display switching button  120   d.  The power supply switching switch  122  is configured to detect a user&#39;s operation to the power supply switching knob  120   b.    
     As shown in  FIG. 13 , a buzzer  124  is disposed in an upper right portion of the front cover  104 . The buzzer  124  is configured to emit an alarm sound when activated by the user pressing the alarm sound button  70  of the right handle  18 . A signal cable  92  (see  FIGS. 8 and 9 ) connecting the switch box  40  to the battery box  8 , a power supply cable  156   a  (see  FIG. 17 ) connecting the battery box  8  to the right headlight  156  and the left headlight  158  (see  FIG. 17 ), a power cable (not shown) connecting the battery box  8  to a motor  150 , and a power cable (not shown) connecting the battery box  8  to the container unit  800  are inserted into a bottom surface of the casing  100 . 
     As shown in  FIG. 15 , a key attachment  128  that is configured to detachably attach a key  126  thereto is disposed on the rear surface of the casing  100 . Attachment/detachment of the key  126  to/from the key attachment  128  is realized by inserting/removing the key  126  to/from the key attachment  128 . Supply of electric power from the battery packs  112  to the motor  150  (which will be described later) is cut off when the key  126  is removed from the key attachment  128 . Supply of electric power from the battery packs  112  to the motor  150  is allowed when the key  126  is attached to the key attachment  128 . 
     (Chassis Frame  10 ) 
     As shown in  FIG. 1 , the chassis frame  10  includes the frame plate  130 , a right frame pipe  132 , a left frame pipe  134 , and a central frame pipe  136 . All of the frame plate  130 , the right frame pipe  132 , the left frame pipe  134 , and the central frame pipe  136  are constituted of a steel material. The frame plate  130  includes a floor plate  130   a  having a substantially rectangular shape where its long side is along the right-left direction and its short side is along the front-rear direction, a front flange  130   b  that is bent downward from a front end of the floor plate  130   a,  and a rear flange  130   c  that is bent downward from a rear end of the floor plate  130   a  (see  FIGS. 36 and 38 ). On a lower surface of the frame plate  130 , multiple reinforcing ribs (not shown) are arranged along the front-rear direction and the right-left direction between the front flange  130   b  and the rear flange  130   c.  The rear wheel unit  14  is attached to the frame plate  130 . Rear ends of the right frame pipe  132  and the left frame pipe  134  are welded to the frame plate  130 , and the right frame pipe  132  and the left frame pipe  134  extend forward. An interval between the right frame pipe  132  and the left frame pipe  134  increases from the rear to the front. Front ends of the left frame pipe  134  and the right frame pipe  132  are attached to the front wheel unit  12 . The central frame pipe  136  is disposed in the vicinity of the front wheel unit  12 , a right end thereof is welded to the right frame pipe  132 , and a left end thereof is welded to the left frame pipe  134 . The power supply cable  156   a  (see  FIG. 17 ) connecting the right headlight  156  and the left headlight  158  to the battery box  8  and a cable cover  138  that protects a power cable (not shown) connecting the battery box  8  to the motor  150  are attached to the right frame pipe  132 . 
     (Front Wheel Unit  12 ) 
     As shown in  FIG. 17 , the front wheel unit  12  includes a right front wheel  140 , a left front wheel  142 , a right front wheel brake  144 , a left front wheel brake  146 , a brake equalizer  148 , the motor  150 , a gearbox  152 , a dead man&#39;s brake  154 , the right headlight  156 , and the left headlight  158 . The right front wheel  140  is connected to the gearbox  152  via a right drive shaft  160  (see  FIGS. 21 and 22 ). The right drive shaft  160  extends in a right axle case  162  along the right-left direction and is rotatably supported by the right axle case  162  via a bearing (not shown). The right axle case  162  is held by the right frame pipe  132  via a right bracket  164  welded to the right frame pipe  132 . The left front wheel  142  is connected to the gearbox  152  via a left drive shaft  166  (see  FIGS. 21 and 22 ). The left drive shaft  166  extends in a left axle case  168  along the right-left direction and is rotatably supported by the left axle case  168  via a bearing (not shown). The left axle case  168  is held by the left frame pipe  134  via a left bracket  170  welded to the left frame pipe  134 . All of the right axle case  162 , the right bracket  164 , the left axle case  168 , and the left bracket  170  are constituted of a steel material. 
     The right front wheel brake  144  includes a disk rotor  172  and a brake caliper  174 . The disk rotor  172  is disposed leftward of the right front wheel  140  and is fixed to the right front wheel  140  via a hub  140   a.  The brake caliper  174  is disposed corresponding to the disk rotor  172 . The brake caliper  174  is held by the right bracket  164 . A right brake cable  176  is connected to the brake caliper  174 . The right brake cable  176  includes an inner cable  176   a  and an outer cable  176   b  covering the periphery of the inner cable  176   a.  When the inner cable  176   a  of the right brake cable  176  is relatively pulled into the outer cable  176   b,  the brake caliper  174  has a pair of brake pads (not shown) sandwiching the vicinity of outer edge of the disk rotor  172 , which applies a frictional force to the disk rotor  172  to brake the right front wheel  140 . When the inner cable  176   a  of the right brake cable  176  is relatively pushed out from the outer cable  176   b,  the pair of brake pads is separated from the disk rotor  172  and the braking on the right front wheel  140  is thereby released. The right front wheel brake  144  may be a so-called disk brake as described above, or may be another type of brake such as a drum brake or a band brake. 
     The left front wheel brake  146  includes a disk rotor  178  and a brake caliper  180 . The disk rotor  178  is disposed rightward of the left front wheel  142  and is fixed to the left front wheel  142  via a hub  142   a.  The brake caliper  180  is disposed corresponding to the disk rotor  178 . The brake caliper  180  is held by the left bracket  170 . A left brake cable  182  is connected to the brake caliper  180 . The left brake cable  182  includes an inner cable  182   a  and an outer cable  182   b  covering the periphery of the inner cable  182   a.  When the inner cable  182   a  of the left brake cable  182  is relatively pulled into the outer cable  182   b,  the brake caliper  180  has a pair of brake pads (not shown) sandwiching the vicinity of outer edge of the disk rotor  178 , which applies a frictional force to the disk rotor  178  to brake the left front wheel  142 . When the inner cable  182   a  of the left brake cable  182  is relatively pushed out from the outer cable  182   b,  the pair of brake pads is separated from the disk rotor  178  and the braking on the left front wheel  142  is thereby released. The left front wheel brake  146  may be a so-called disk brake as described above, or may be another type of brake, such as a drum brake or a band brake. 
     (Brake Equalizer  148 ) 
     As shown in  FIG. 18 , the brake equalizer  148  includes a central bracket  184 , a first link member  186 , and a second link member  188 . The central bracket  184  is constituted of a steel material, and the first link member  186  and the second link member  188  are both constituted of an aluminum material. The central bracket  184  is welded to the vicinity of the center of the central frame pipe  136 . The first link member  186  and the second link member  188  are pivotably supported by the central bracket  184  via a pivot axis  190  extending in the up-down direction. The first link member  186  includes an input arm  186   a  extending rightward and forward from the pivot axis  190  and an output arm  186   b  extending rightward and rearward from the pivot axis  190 . A distal end of the input arm  186   a  is connected to the inner cable  94   a  of the brake cable  94  extending from the brake lever  49  of the left handle  20 . A distal end of the output arm  186   b  is connected to the inner cable  176   a  of the right brake cable  176 . The second link member  188  includes an input arm  188   a  extending rightward and forward from the pivot axis  190  and an output arm  188   b  extending leftward and rearward from the pivot axis  190 . A distal end of the input arm  188   a  is connected to the outer cable  94   b  of the brake cable  94  extending from the brake lever  49  of the left handle  20 . A distal end of the output arm  188   b  is connected to the inner cable  182   a  of the left brake cable  182 . The outer cable  176   b  of the right brake cable  176  and the outer cable  182   b  of the left brake cable  182  are both fixed to the central bracket  184 . In another embodiment, the first link member  186  and the second link member  188  may be pivotably supported by the central bracket  184  via a pivot axis extending in the right-left direction or in the front-rear direction. 
     A distance from the pivot axis  190  to the distal end of the input arm  186   a,  a distance from the pivot axis  190  to the distal end of the output arm  186   b,  and an angle formed by the input arm  186   a  and the output arm  186   b  in the first link member  186  are substantially the same as a distance from the pivot axis  190  to the distal end of the input arm  188   a,  a distance from the pivot axis  190  to the distal end of the output arm  188   b,  and an angle formed by the input arm  188   a  and the output arm  188   b  in the second link member  188 . 
     As shown in  FIG. 19 , when the brake lever  49  of the left handle  20  is not pushed up by the user, the inner cable  176   a  of the right brake cable  176  is relatively pushed into the outer cable  176   b  by the first link member  186  and the inner cable  182   a  of the left brake cable  182  is relatively pushed into the outer cable  182   b  by the second link member  188 . In this state, the brake on the right front wheel  140  and the left front wheel  142  is released. 
     As shown in  FIG. 20 , when the brake lever  49  of the left handle  20  is pushed up by the user, the inner cable  94   a  of the brake cable  94  is relatively pulled into the outer cable  94   b.  This moves the input arm  186   a  of the first link member  186  rightward and the output arm  186   b  leftward, as a result of which the inner cable  176   a  of the right brake cable  176  is relatively pulled out from the outer cable  176   b.  At the same time, the input arm  188   a  of the second link member  188  is moved leftward and the output arm  188   b  is moved rightward, as a result of which the inner cable  182   a  of the left brake cable  182  is relatively pulled out from the outer cable  182   b.  As above, the right front wheel  140  and the left front wheel  142  are braked. 
     Due to adjustment error between the right front wheel brake  144  and the left front wheel brake  146  and/or age deterioration of the right brake cable  176  and the left brake cable  182 , the right front wheel brake  144  and the left front wheel brake  146  may operate differently even though the right brake cable  176  and the left brake cable  182  are the same in the pulled-out amount. For example, when the inner cable  94   a  of the brake cable  94  is relatively pulled into the outer cable  94   b,  the brake pads contact the disk rotor  172  in the right front wheel brake  144 , whereas the brake pads may not contact the disk rotor  178  in the left front wheel brake  146 . In such a state, when the inner cable  94   a  of the brake cable  94  is further pulled into the outer cable  94   b,  the first link member  186  does not pivot any more but the second link member  188  further pivots, which brings the brake pads into contact with the disk rotor  178  in the left front wheel brake  146 . As described, the brake equalizer  148  of this embodiment can cancel out imbalance of tensions acting on the right brake cable  176  and the left brake cable  182  by the pivoting of the first link member  186  and the second link member  188 , and can balance out the braking force applied to the right front wheel brake  144  and the braking force applied to the left front wheel brake  146 . 
     The brake equalizer  148  may be configured as shown in  FIG. 56 . In the configuration shown in  FIG. 56 , the brake equalizer  148  includes a central bracket  184 , a first link member  802 , and a second link member  804 . A front end of the first link member  802  and a front end of the second link member  804  are pivotably supported by the central bracket  184  via a pivot axis  806  extending in the up-down direction. The inner cable  182   a  of the left brake cable  182  is connected to a rear end of the first link member  802 . The inner cable  176   a  of the right brake cable  176  is connected to a rear end of the second link member  804 . The outer cable  176   b  of the right brake cable  176  and the outer cable  182   b  of the left brake cable  182  are both fixed to the central bracket  184 . The inner cable  94   a  of the brake cable  94  is connected to the vicinity of the center of the first link member  802 . The outer cable  94   b  of the brake cable  94  is connected to the vicinity of the center of the second link member  804 . A distance from the pivot axis  806  to the position where the inner cable  94   a  is retained and a distance from the pivot axis  806  to the position where the inner cable  182   a  is retained in the first link member  802  are substantially the same as a distance from the pivot axis  806  to the position where the outer cable  94   b  is retained and a distance from the pivot axis  806  to the position where the inner cable  176   a  is retained in the second link member  804 , respectively. 
     When the brake lever  49  of the left handle  20  is not pushed up by the user, the inner cable  182   a  of the left brake cable  182  is relatively pushed in the outer cable  182   b  by the first link member  802  and the inner cable  176   a  of the right brake cable  176  is relatively pushed in the outer cable  176   b  by the second link member  804 . In this state, the brake on the right front wheel  140  and the left front wheel  142  is released. 
     When the brake lever  49  of the left handle  20  is pushed up by the user, the inner cable  94   a  of the brake cable  94  is relatively pulled into the outer cable  94   b.  This causes the first link member  802  to rotate rightward, thus the inner cable  182   a  of the left brake cable  182  is thereby relatively pulled out from the outer cable  182   b.  At the same time, the second link member  804  rotates leftward, thus the inner cable  176   a  of the right brake cable  176  is thereby relatively pulled out from the outer cable  176   b.  As a result, the right front wheel  140  and the left front wheel  142  are braked. As described, the configuration shown in  FIG. 56  can also cancel out the imbalance of tensions acting on the right brake cable  176  and the left brake cable  182  by the pivoting of the first link member  802  and the second link member  804 , and can balance out the braking force applied to the right front wheel brake  144  and the braking force applied to the left front wheel brake  146 . 
     Alternatively, the brake equalizer  148  may be configured as shown in  FIG. 57 . In the configuration shown in  FIG. 57 , the brake equalizer  148  includes the central bracket  184 , a first link member  808 , and a second link member  810 . The first link member  808  is pivotably supported by the central bracket  184  via a pivot axis  812  extending in the up-down direction. The second link member  810  is pivotably supported by the central bracket  184  via a pivot axis  814  extending in the up-down direction. The inner cable  176   a  of the right brake cable  176  is connected to a rear end of the first link member  808 . The inner cable  182   a  of the left brake cable  182  is connected to a rear end of the second link member  810 . The outer cable  176   b  of the right brake cable  176  and the outer cable  182   b  of the left brake cable  182  are both fixed to the central bracket  184 . The inner cable  94   a  of the brake cable  94  is connected to a front end of the first link member  808 . The outer cable  94   b  of the brake cable  94  is connected to a front end of the second link member  810 . A distance from the pivot axis  812  to the position where the inner cable  94   a  is retained and a distance from the pivot axis  812  to the position where the inner cable  176   a  is retained in the first link member  808  are substantially the same as a distance from the pivot axis  814  to the position where the outer cable  94   b  is retained and a distance from the pivot axis  814  to the position where the inner cable  182   a  is retained in the second link member  810 , respectively. 
     When the brake lever  49  of the left handle  20  is not pushed up by the user, the inner cable  176   a  of the right brake cable  176  is relatively pushed into the outer cable  176   b  by the first link member  808 , and the inner cable  182   a  of the left brake cable  182  is relatively pushed into the outer cable  182   b  by the second link member  810 . In this state, the brake on the right front wheel  140  and the left front wheel  142  is released. 
     When the brake lever  49  of the left handle  20  is pushed up by the user, the inner cable  94   a  of the brake cable  94  is relatively pulled into the outer cable  94   b.  This causes the first link member  808  to pivot such that its front end moves rightward and its rear end moves leftward, thus the inner cable  176   a  of the right brake cable  176  is relatively pulled out from the outer cable  176   b.  At the same time, the second link member  810  pivots such that its front end moves leftward and its rear end moves rightward, thus the inner cable  182   a  of the left brake cable  182  is relatively pulled out from the outer cable  182   b.  As a result, the right front wheel  140  and the left front wheel  142  are braked. As described, the configuration of  FIG. 57  can also cancel out the imbalance of tensions acting on the right brake cable  176  and the left brake cable  182  by the pivoting of the first link member  808  and the second link member  810 , and can balance out the braking force applied to the right front wheel brake  144  and the braking force applied to the left front wheel brake  146 . 
     (Motor  150 ) 
     As shown in  FIG. 21 , the motor  150  includes a stator  192 , a rotor  194 , and a motor case  196 . The motor  150  is, for example, a brushless DC motor. The stator  192  and the rotor  194  are housed in the motor case  196 . The motor case  196  is constituted of an aluminum material. The stator  192  is fixed to the motor case  196 . The rotor  194  is fixed to a motor shaft  198 . The motor shaft  198  extends in the right-left direction and is rotatably supported by the motor case  196  via bearings  198   a  and  198   b.  A left end of the motor shaft  198  is connected to the gearbox  152 . A right end of the motor shaft  198  is located outside of the motor case  196  and is connected to the dead man&#39;s brake  154 . The motor  150  is connected to the battery box  8  via a power cable (not shown). The motor  150  is supplied with power from the battery packs  112 . Operation of the motor  150  is controlled by the control board  108 . 
     (Gearbox  152 ) 
     The gearbox  152  includes a gear case  200 , an intermediate shaft  202 , a clutch mechanism  206 , and a differential mechanism  208 . The gear case  200  is constituted of an aluminum material. The right axle case  162 , the left axle case  168 , and the gear case  200  are fixed with screws. The motor case  196  is screwed and fixed to the gear case  200 . The gear case  200  is screwed and fixed to the central bracket  184  of the central frame pipe  136  via a support bracket (not shown). 
     The intermediate shaft  202  extends in the right-left direction and is rotatably supported by the gear case  200  via bearings  202   a  and  202   b.  The intermediate shaft  202  includes a first gear  203 , a second gear  204 , and a dog clutch  205 . The first gear  203  is fixed to the intermediate shaft  202 . The first gear  203  meshes with a spur gear  198   c  disposed on the motor shaft  198 . The first gear  203  includes an engagement recess  203   a  that is recessed rightward. 
     The second gear  204  is immovable in the right-left direction with respect to the intermediate shaft  202  and is rotatably supported by the intermediate shaft  202 . The dog clutch  205  is movable in the right-left direction with respect to the second gear  204  and is supported by the second gear  204  in a non-rotatable manner. The dog clutch  205  includes an engagement projection  205   a  that projects rightward and is configured to engage with the engagement recess  203   a  of the first gear  203  and an engagement groove  205   b  that circumferentially extends in an outer circumferential surface of the dog clutch  205 . 
     The clutch mechanism  206  includes a clutch lever  210 , a support bracket  212 , a rod  214 , and a selector  216 . The clutch lever  210  and the support bracket  212  are disposed outside the gear case  200 . The support bracket  212  is screwed and fixed to the gear case  200 . The clutch lever  210  is pivotably supported by the support bracket  212  about a pivot axis  210   a.  The clutch lever  210  includes a cam surface  210   b.  The rod  214  extends in the right-left direction and penetrates the gear case  200  from the inside to the outside thereof. The rod  214  is supported by the gear case  200  and is slidable in the right-left direction. A left end of the rod  214  is located to face the cam surface  210   b  of the clutch lever  210 . The selector  216  is fixed to a right end of the rod  214 , and the selector  216  is engaged with the engagement groove  205   b  of the dog clutch  205 . The rod  214  is biased leftward with respect to the gear case  200  by a compression spring (not shown). Thus, the left end of the rod  214  is always in contact with the cam surface  210   b  of the clutch lever  210 . The cam surface  210   b  of the clutch lever  210  has a shape that allows the rod  214  to move leftward when the clutch lever  210  is pushed toward the support bracket  212  (see  FIG. 21 ) and allows the rod  214  to move rightward when the clutch lever  210  is pulled away from the support bracket  212  (see  FIG. 22 ). 
     The differential mechanism  208  includes a ring gear  208   a,  a pinion case  208   b,  a pinion shaft  208   c,  a pinion gear  208   d,  a right drive gear  208   e,  and a left drive gear  208   f  The ring gear  208   a  meshes with the second gear  204  of the intermediate shaft  202 . The pinion case  208   b  is screwed and fixed to the ring gear  208   a  and rotates integrally with the ring gear  208   a.  The ring gear  208   a  is rotatably supported by the gear case  200  via a bearing  208   g,  and the pinion case  208   b  is rotatably supported by the gear case  200  via a bearing  208   h.  The pinion shaft  208   c  is rotatably supported by the pinion case  208   b.  The pinion gear  208   d  is fixed to the pinion shaft  208   c.  The right drive gear  208   e  is fixed to the right drive shaft  160  and meshes with the pinion gear  208   d.  The left drive gear  208   f  is fixed to the left drive shaft  166  and meshes with the pinion gear  208   d.    
     As shown in  FIG. 21 , when the clutch lever  210  of the clutch mechanism  206  is pushed down, the rod  214  and the selector  216  moves leftward and the engagement projection  205   a  of the dog clutch  205  separates from the engagement recess  203   a  of the first gear  203 . In this state, the second gear  204  does not rotate even when the first gear  203  rotates. Thus, power from the motor shaft  198  is not transmitted to the ring gear  208   a  of the differential mechanism  208 . In this case, when one of the right drive shaft  160  and the left drive shaft  166  rotates, the differential mechanism  208  rotates the other of the right drive shaft  160  and the left drive shaft  166  at the same rotational speed in the opposite direction. 
     As shown in  FIG. 22 , when the clutch lever  210  of the clutch mechanism  206  is pulled up, the rod  214  and the selector  216  moves rightward and the engagement projection  205   a  of the dog clutch  205  engages with the engagement recess  203   a  of the first gear  203 . In this state, the second gear  204  rotates when the first gear  203  rotates. Thus, the power from the motor shaft  198  is transmitted to the ring gear  208   a  of the differential mechanism  208  via the intermediate shaft  202 . In this case, the differential mechanism  208  rotates the right drive shaft  160  and the left drive shaft  166  according to the power transmitted to the ring gear  208   a.    
     (Dead Man&#39;s Brake  154 ) 
     As shown in  FIG. 23 , the dead man&#39;s brake  154  includes a disk rotor  218  and a brake caliper  220 . The disk rotor  218  is fixed to the right end of the motor shaft  198  of the motor  150 . Although not shown in  FIG. 23 , the disk rotor  218  is covered by a disk cover  218   a  (see  FIGS. 21 and 22 ) fixed to the motor case  196 . The brake caliper  220  is disposed corresponding to the disk rotor  218 . The brake caliper  220  is supported by the motor case  196 . The dead man&#39;s cable  90  extending from the right handle  18  is connected to the brake caliper  220 . The brake caliper  220  biases a pair of brake pads (not shown) by a return spring (not shown) in a direction that brings the pair to sandwich the vicinity of outer edge of the disk rotor  218 . Thus, when the inner cable  90   a  of the dead man&#39;s cable  90  is relatively pushed out from the outer cable  90   b,  the pair of brake pads sandwich the vicinity of the outer edge of the disk rotor  218 , which applies a frictional force to the disk rotor  218  and brakes the motor shaft  198 . When the inner cable  90   a  of the dead man&#39;s cable  90  is relatively pulled into the outer cable  90   b,  the pair of brake pads separates away from the disk rotor  218  against the biasing force of the return spring, which releases the brake on the motor shaft  198 . The dead man&#39;s brake  154  may be a so-called disk brake as described above, or may be another type of brake such as a drum brake or a band brake. 
     While the right front wheel  140  and left front wheel  142  are rotated by the power of the motor  150 , the motor shaft  198  is rotated at high rotational speed and low torque, whereas the right drive shaft  160  and left drive shaft  166  are rotated at low rotational speed and high torque. Since braking the motor shaft  198  by the dead man&#39;s brake  154  requires small torque for the brake as compared to braking the right front wheel  140  by the right front wheel brake  144  and braking the left front wheel  142  by the left front wheel brake  146 , it can surely stop the rotation of the right front wheel  140  and the left front wheel  142 . 
     The motor  150 , the gearbox  152 , and the dead man&#39;s brake  154  may be configured as shown in  FIGS. 58 and 59 . In this configuration, the right end of the motor shaft  198  is not located outside of the motor case  196 . Further, a brake disk  850  is fixed to the left end of the motor shaft  198 . 
     In the configuration shown in  FIGS. 58 and 59 , the gearbox  152  includes the gear case  200 , a relay shaft  852 , the differential mechanism  208 , a differential lock mechanism  854 , and a brake mechanism  856 . In this configuration, the brake disk  850  and the brake mechanism  856  configure the dead man&#39;s brake  154 . The relay shaft  852  extends in the right-left direction and is rotatably supported by the gear case  200  via bearings  852   a  and  852   b.  The relay shaft  852  includes a spur gear  852   c  and a spur gear  852   d.  The spur gear  852   c  meshes with the spur gear  198   c  disposed on the motor shaft  198 . The spur gear  852   d  meshes with the ring gear  208   a  of the differential mechanism  208 . 
     The differential lock mechanism  854  includes a dog clutch  858  and a compression spring  860 . The dog clutch  858  is slidable in the right-left direction with respect to the left drive shaft  166  and is supported by the left drive shaft  166  to rotate integrally with the left drive shaft  166 . The dog clutch  858  includes an engagement projection  858   a  projecting rightward and an engagement groove  858   b  circumferentially extending in an outer circumferential surface of dog clutch  858 . In this configuration, the ring gear  208   a  of the differential mechanism  208  includes an engagement recess  208   i  configured to engage with the engagement projection  858   a  of the dog clutch  858 . The compression spring  860  biases the dog clutch  858  rightward (i.e., in a direction that brings the dog clutch  858  close to the ring gear  208   a ) with respect to the gear case  200 . 
     The brake mechanism  856  includes a rod  862 , a brake plate  864 , and a compression spring  866 . The rod  862  extends in the right-left direction and penetrates the gear case  200  from the inside to the outside thereof. The rod  862  is supported by the gear case  200  and is slidable in the right-left direction. The inner cable  90   a  of the dead man&#39;s cable  90  is connected to a left end of the rod  862 . The outer cable  90   b  of the dead man&#39;s cable  90  is connected to the gear case  200 . The brake plate  864  is fixed to a right end of the rod  862 . The brake plate  864  is provided with a brake shoe  864   a  disposed corresponding to the brake disk  850  and a selector  864   b  configured to engage with the engagement groove  858   b  of the dog clutch  858 . The compression spring  866  biases the brake plate  864  rightward (i.e., in a direction that brings the brake plate  864  close to the brake disk  850 ) with respect to the gear case  200 . 
     As shown in  FIG. 59 , when the inner cable  90   a  of the dead man&#39;s cable  90  is relatively pushed out from the outer cable  90   b,  the rod  862  and the brake plate  864  is moved rightward by the biasing force of the compression spring  866  and the brake shoe  864   a  is pressed against the brake disk  850 . This applies a frictional force to the brake disk  850  and brakes the motor shaft  198 . Further, when the selector  864   b  disposed on the brake plate  864  is moved rightward, the dog clutch  858  is also moved rightward by the biasing force of the compression spring  860  and the engagement projection  858   a  of the dog clutch  858  engages with the engagement recess  208   i  of the ring gear  208   a.  In this case, at the differential mechanism  208 , the ring gear  208   a  is fixed to the left drive shaft  166 , and the right drive shaft  160  and the left drive shaft  166  rotate at the same rotational speed in the same direction. Braking the rotation of the motor shaft  198  by the dead man&#39;s brake  154  results in braking the rotation of the ring gear  208   a,  thereby braking the rotation of the right drive shaft  160  and the left drive shaft  166 . 
     As shown in  FIG. 58 , when the inner cable  90   a  of the dead man&#39;s cable  90  is relatively pulled into the outer cable  90   b,  the rod  862  and the brake plate  864  are moved leftward and the brake shoe  864   a  is separated away from the brake disk  850 . This releases the brake on the motor shaft  198 . Further, when the selector  864   b  disposed on the brake plate  864  is moved leftward, the dog clutch  858  is also moved leftward and the engagement projection  858   a  of the dog clutch  858  is separated from the engagement recess  208   i  of the ring gear  208   a.  In this case, the differential mechanism  208  rotates the right drive shaft  160  and the left drive shaft  166  according to the power transmitted from the motor shaft  198  to the ring gear  208   a  via the relay shaft  852 . 
     (Right Headlight  156  and Left Headlight  158 ) 
     As shown in  FIG. 17 , the right headlight  156  is supported by the right bracket  164 . The right headlight  156  is connected to the battery box  8  via the power supply cable  156   a.  The left headlight  158  is supported by the left bracket  170 . The left headlight  158  is connected to the right headlight  156  via a relay cable  158   a.  The right headlight  156  and the left headlight  158  are supplied with electric power from the battery packs  112 . Operations of the right headlight  156  and the left headlight  158  are controlled by the control board  108 . 
     (Rear Wheel Unit  14 ) 
     As shown in  FIGS. 24, 25, and 26 , the rear wheel unit  14  includes a base plate  222 , a hinge  224 , a right caster  226 , and a left caster  228 . The base plate  222  and the hinge  224  are both constituted of a steel material. The base plate  222  includes a web  222   a  extending along the front-rear direction and the right-left direction, a front flange  222   b  bent downward from a front end of the web  222   a,  and a rear flange  222   c  bent downward from a rear end of the web  222   a.  The hinge  224  includes a support pipe  224   a  extending in the front-rear direction, a front support plate  224   b  extending in the up-down direction and the right-left direction, and a rear support plate  224   c  extending in the up-down direction and the right-left direction. The front support plate  224   b  has a substantially triangular shape and is welded to the vicinity of a front end of the support pipe  224   a  with the support pipe  224   a  penetrating the center of the front support plate  224   b.  The rear support plate  224   c  has a substantially triangular shape and is welded to the vicinity of a rear end of the support pipe  224   a  with the support pipe  224   a  penetrating the center of the rear support plate  224   c.  Lower ends of the front support plate  224   b  and the rear support plate  224   c  are welded to an upper surface of the web  222   a  of the base plate  222 . In the following description, the base plate  222  and the hinge  224  may be collectively referred to as a rear wheel frame  225 . 
     (Right Caster  226 ) The right caster  226  includes a center pin  230 , a top plate  232 , a bracket  234 , a wheel shaft  236 , a right rear wheel  238 , and a lock mechanism  240 . 
     As shown in  FIG. 27 , the center pin  230  penetrates the web  222   a  of the base plate  222  in the up-down direction. The center pin  230  is rotatably supported by the top plate  232  via a bearing  230   a.  The top plate  232  is screwed and fixed to the base plate  222  with an upper surface of the top plate  232  being in contact with a lower surface of the web  222   a  of the base plate  222 . The bracket  234  includes a retainer  234   a,  a right arm  234   b,  and a left arm  234   c.  The retainer  234   a,  the right arm  234   b,  and the left arm  234   c  are configured integrally. The center pin  230  penetrates the retainer  234   a  in the up-down direction. The retainer  234   a  is fixed to a lower end of the center pin  230 . The retainer  234   a  is rotatably supported by the top plate  232  via a bearing  234   d.  The right arm  234   b  extends rearward and downward from a right end of the retainer  234   a.  The left arm  234   c  extends rearward and downward from a left end of the retainer  234   a.    
     As shown in  FIG. 28 , the wheel shaft  236  extends in the right-left direction. The wheel shaft  236  is configured of a bolt  236   a  that penetrates a distal end portion of the left arm  234   c  to a distal end portion of the right arm  234   b  and a nut  236   b  that is screwed to the bolt  236   a  from the distal end side of the right arm  234   b.  A right end of the wheel shaft  236  is fixed to the distal end of the right arm  234   b,  and a left end of the wheel shaft  236  is fixed to the distal end of the left arm  234   c.  The right rear wheel  238  includes a first right rear wheel  238   a  and a second right rear wheel  238   b.  The first right rear wheel  238   a  is rotatably supported by the wheel shaft  236  via a bearing  238   c.  The second right rear wheel  238   b  is rotatably supported by the wheel shaft  236  via a bearing  238   d.  That is, the first right rear wheel  238   a  and the second right rear wheel  238   b  are rotatable about a rotation axis RX 2 , which is a central axis of the wheel shaft  236 , independently of each other. Diameters of the first right rear wheel  238   a  and the second right rear wheel  238   b  are, for example, 200 mm, and widths of the first right rear wheel  238   a  and the second right rear wheel  238   b  are, for example, 100 mm. An interval between the first right rear wheel  238   a  and the second right rear wheel  238   b  is, for example, 6 mm±2 mm. 
     As shown in  FIG. 61 , the wheel shaft  236  may be configured of a sleeve  236   c  that penetrates the distal end portion of the left arm  234   c  and the distal end portion of the right arm  234   b  and includes a threaded inner surface, a bolt  236   d  that is screwed into the sleeve  236   c  from the distal end side of the right arm  234   b,  and a bolt  236   e  that is screwed into the sleeve  236   c  from the distal end side of the left arm  234   c.  In the configuration in which the wheel shaft  236  is configured of the bolt  236   a  and the nut  236   b  as shown in  FIG. 28 , the tip of the bolt  236   a  protrudes from the nut  236   b  when the nut  236   b  is screwed to the bolt  236   a,  which results in increased protrusion from the bracket  234  and may diminish the aesthetic appearance of the product. The configuration in which the wheel shaft  236  is configured of the sleeve  236   c  and the bolts  236   d  and  236   e,  as shown in  FIG. 61 , can reduce the protrusion from the bracket  234  and improves the aesthetic appearance of the product. 
     In the right caster  226 , the bracket  234 , the wheel shaft  236 , and the right rear wheel  238  integrally pivot, with respect to the top plate  232 , on a pivot axis RX 1  which is a central axis of the center pin  230 . Thus, a traveling direction of the right rear wheel  238  can be changed in accordance with a traveling direction of the rear wheel unit  14 . 
     As shown in  FIGS. 34 and 35 , in a top plan view of the right caster  226 , the rotation axis RX 2 , which is the central axis of the wheel shaft  236 , is offset from the pivot axis RX 1 , which is the central axis of the center pin  230 . A distance from the pivot axis RX 1  to the rotation axis RX 2  in the top plan view of the right caster  226  is, for example, within a range of 50 mm to 60 mm, and the distance is, for example, 55 mm. 
     As shown in  FIG. 27 , the lock mechanism  240  includes a lock pin  242 , a support plate  244 , and a compression spring  246 . The lock pin  242  is a substantially L-shaped rod member. The lock pin  242  includes a first shaft portion  242   a  extending in the up-down direction and a second shaft portion  242   b  that is bent at an upper end of the first shaft portion  242   a.  The support plate  244  is screwed and fixed to the upper surface of the web  222   a  of the base plate  222 . As shown in  FIG. 29 , the support plate  244  includes a through hole  244   a  through which the first shaft portion  242   a  of the lock pin  242  passes in the up-down direction. An upper end of the support plate  244  is provided with a first retainer portion  244   b  configured to retain the second shaft portion  242   b  of the lock pin  242  at a first height and a second retainer portion  244   c  configured to retain the second shaft portion  242   b  of the lock pin  242  at a second height that is lower than the first height. As shown in  FIG. 27 , the compression spring  246  biases the lock pin  242  downward relative to the support plate  244 . 
     As shown in  FIGS. 30 and 31 , the top plate  232  is provided with a through hole  232   a  through which the first shaft portion  242   a  of the lock pin  242  passes. Engagement grooves  234   e  with which the first shaft portion  242   a  of the lock pin  242  engages are disposed in the retainer  234   a  of the bracket  234  at predetermined angular intervals. As shown in  FIG. 30 , when the second shaft portion  242   b  of the lock pin  242  is retained by the first retainer portion  244   b  of the support plate  244 , the first shaft portion  242   a  of the lock pin  242  is through the through hole  232   a  of the top plate  232  but is not engaged with any of the engagement grooves  234   e  of the bracket  234 . This state allows the bracket  234 , the wheel shaft  236 , and the right rear wheel  238  to integrally pivot with respect to the top plate  232 . The position of the lock pin  242  in this state may be referred to as an unlocked position. As shown in  FIG. 31 , when the second shaft portion  242   b  of the lock pin  242  is retained by the second retainer portion  244   c  of the support plate  244 , the first shaft portion  242   a  of the lock pin  242  is through the through hole  232   a  of the top plate  232  and is further engaged with one of the engagement grooves  234   e  of the bracket  234 . This state prohibits the bracket  234 , the wheel shaft  236 , and the right rear wheel  238  from integrally pivoting with respect to the top plate  232 . The position of the lock pin  242  in this state may be referred to as a locking position. By switching the position of the lock pin  242  between the locking position and the unlocked position, the user of the cart  2  can switch the state of right caster  226  between the state that allows the integral pivoting of the bracket  234 , the wheel shaft  236 , and the right rear wheel  238  and the state that prohibits the integral pivoting. 
     For a configuration in which the right rear wheel  238  includes only a single wheel  238   e,    FIG. 32  shows a positional relationship between the center pin  230 , the wheel shaft  236 , and the wheel  238   e  in the top view of the right caster  226 . For example, when the right rear wheel  238  obliquely collides with a bump S, the right rear wheel  238  would easily cross over the bump S if the wheel shaft  236  and the wheel  238   e  are pivoted such that the traveling direction of the wheel  238   e  becomes perpendicular to the bump S as shown in  FIG. 33 . However, torque T, which is due to the force the wheel  238   e  receives from the bump S shown in  FIG. 32 , acts in the opposite direction to the above-mentioned pivot direction, thus the wheel  238   e  pivots such that a side surface of the wheel  238   e  comes into contact with the bump S as shown in  FIG. 60 . With the wheel  238   e  pivoted as such, the right rear wheel  238  cannot cross over the bump S. 
     On the other hand, in the cart  2  of the present embodiment, the right rear wheel  238  includes the first right rear wheel  238   a  and the second right rear wheel  238   b  as shown in  FIG. 34 . For example, when the right rear wheel  238  obliquely collides with the bump S, the right rear wheel  238  would easily cross over the bump S if the first right rear wheel  238   a  and the second right rear wheel  238   b  pivot such that the traveling direction of the first right rear wheel  238   a  and the second right rear wheel  238   b  becomes perpendicular to the bump S as shown in  FIG. 35 . In the present embodiment, torque T, which is due to the force the second right rear wheel  238   b  receives from the bump S shown in  FIG. 34 , acts in the same direction as the above-mentioned pivot direction, thus the right rear wheel  238  can easily cross over the bump S. 
     In the cart  2  of the present embodiment, the first right rear wheel  238   a  and the second right rear wheel  238   b  are rotatable to the wheel shaft  236  independent of each other. Thus, as shown in  FIG. 34 , for example, when the right rear wheel  238  obliquely collides with the bump S and the second right rear wheel  238   b  comes into contact with the bump S, rotating the first right rear wheel  238   a,  which is not in contact with the bump S, relative to the second right rear wheel  238   b  can easily change the traveling direction of the right rear wheel  238  to become perpendicular to the bump S as shown in  FIG. 35 , and the right rear wheel  238  can thereby easily cross over the bump S. 
     (Left Caster  228 ) 
     Similar to the right caster  226 , the left caster  228  includes a center pin  250 , a top plate  252 , a bracket  254 , a shaft  256 , a left rear wheel  258 , and a lock mechanism  260 . The bracket  254  includes a retainer  254   a,  a right arm  254   b,  and a left arm  254   c.  The left rear wheel  258  includes a first left rear wheel  258   a  and a second left rear wheel  258   b.  The lock mechanism  260  includes a lock pin  262 , a support plate  264 , and a compression spring  266 . Detailed description for the configuration of the left caster  228  is omitted because it is the same as horizontally inverted configuration of the right caster  226 . 
     (Coupling Site of Rear Wheel Unit  14  and Chassis Frame  10 ) 
     As shown in  FIG. 36 , the rear wheel unit  14  is connected to the chassis frame  10  via a coupling shaft  270  extending in the front-rear direction. As shown in  FIG. 37 , a coupling pipe  272  and a support plate  274  are welded to the lower surface of the frame plate  130  of the chassis frame  10 . The coupling pipe  272  extends along the front-rear direction, a front end thereof penetrates the support plate  274 , and a rear end thereof penetrates the rear flange  130   c.  The coupling shaft  270  includes a head  270   a  and a shaft  270   b.  The shaft  270   b  of the coupling shaft  270  is inserted into the support pipe  224   a  of the rear wheel unit  14  from the rear and penetrates the support pipe  224   a,  and further penetrates the coupling pipe  272  of the chassis frame  10 . A front end of the coupling shaft  270  is fixed to the support plate  274  with a coupling pin  276 . 
     The support pipe  224   a  is slidable relative to the coupling shaft  270 . Thus, as shown in  FIG. 38 , the rear wheel unit  14  is supported by the chassis frame  10  such that it is swingable about a swing axis PX which is a central axis of the coupling shaft  270 . This configuration allows the rear wheel unit  14  to swing with respect to the chassis frame  10  when the cart  2  travels on an uneven surface, which helps the cart  2  to well follow the surface. Further, as shown in  FIG. 10 , in a rear plan view of the chassis unit  4 , the swing axis PX of the rear wheel unit  14  is located above a straight line L passing through an upper end of the right rear wheel  238  and an upper end of the left rear wheel  258 . This secures the minimum ground clearance and suppresses vibrations of the chassis frame  10  while the cart  2  travels. As shown in  FIG. 38 , the rear flange  130   c  of the chassis frame  10  is provided with a right stopper surface  130   d  located rightward of the coupling shaft  270  and a left stopper surface  130   e  located leftward of the coupling shaft  270 . The right stopper surface  130   d  is inclined upward from the left toward the right. The right stopper surface  130   d  contacts the floor plate  130   a  of the chassis frame  10  when the rear wheel unit  14  swings with respect to the chassis frame  10  in a direction that moves the right rear wheel  238  upward, thereby limiting the swing angle of the rear wheel unit  14  with respect to the chassis frame  10 . The left stopper surface  130   e  is inclined upward from the right to the left. The left stopper surface  130   e  contacts the floor plate  130   a  of the chassis frame  10  when the rear wheel unit  14  swings with respect to the chassis frame  10  in a direction that moves the left rear wheel  258  upward, thereby limiting the swing angle of the rear wheel unit  14  with respect to the chassis frame  10 . In another embodiment, the rear wheel unit  14  may be supported by the chassis frame  10  such that it is not swingable about the swing axis PX with respect to the chassis frame  10 . 
     In the chassis unit  4  of the present embodiment, the right front wheel  140  and the left front wheel  142  are drive wheels, while the right rear wheel  238  and the left rear wheel  258  are non-drive wheels. In another embodiment, the right front wheel  140  and/or the left front wheel  142  may be non-drive wheel(s), and the right rear wheel  238  and/or the left rear wheel  258  may be drive wheel(s). Further, in another embodiment, one of the front wheel unit  12  and the rear wheel unit  14  may include only one wheel, and the other of the front wheel unit  12  and the rear wheel unit  14  may include a plurality of wheels. In yet another embodiment, the chassis unit  4  may not include the rear wheel unit  14 , and the front wheel unit  12  may include only one drive wheel. In yet another embodiment, the chassis unit  4  may include a crawler that is driven by a prime mover, instead of the right front wheel  140 , the left front wheel  142 , the right rear wheel  238  and the left rear wheel  258 . 
     In the chassis unit  4  of the present embodiment, the prime mover for rotating the drive wheel(s) is the motor  150 , and the motor  150  is driven by the power from the battery packs  112  in the battery box  8 . In another embodiment, the prime mover for rotating the drive wheel(s) may be an engine. In yet another embodiment, the motor  150  may be driven by power supplied via a power cord from an external power supply. In yet another embodiment, the motor  150  may be a motor other than a brushless motor, such as a motor with brush. In yet another embodiment, the motor  150  may be an in-wheel motor corresponding to each of the drive wheel(s). 
     The chassis unit  4  of the present embodiment includes the right handle  18  and the left handle  20  which extend in the up-down direction on the right side and the left side of the user, of which upper ends are bent rearward, and of which rear ends are provided with the grips  38  and  48 . In another embodiment, the chassis unit  4  may include a so-called looped handle in which support portions extend in the up-down direction on the right side and the left side of the user and upper ends of the support portions are connected by a grip portion extending in the right-left direction. In this case, the taillight  74  may be disposed on the support portion on the right side of the user and/or the support portion on the left side of the user, and/or may be disposed in the vicinity of right end and/or left end of the grip portion extending in the right-left direction. Alternatively, the chassis unit  4  may include a so-called T-shaped handle in which a support portion extends in the up-down direction at the center in the right-left direction and an upper end of the support portion is connected to a grip portion extending in the right-left direction. In this case, the taillight  74  may be disposed in the vicinity of right end and/or left end of the grip portion extending in the right-left direction. 
     (First Container Unit  300 ) 
     As shown in  FIGS. 39 and 40 , the first container unit  300  includes a container  302 , a right guard  304 , a left guard  306 , a front guard  308 , a rear guard  310 , first arms  312 , second arms  314 , an actuator  316 , and a support base  318 . The support base  318  of the first container unit  300  is screwed and fixed to the chassis unit  4 . The first container unit  300  is configured to move the container  302  in the up-down direction relative to the support base  318  by the actuator  316 . 
     As shown in  FIGS. 39, 40, and 41 , the container  302  includes a container plate  320 , a right channel  322 , a left channel  324 , reinforcement channels  326 , right guard retaining portions  328 , left guard retaining portions  330 , and front guard retaining portions  332 . All of the container plate  320 , the right channel  322 , the left channel  324 , the reinforcement channels  326 , the right guard retaining portions  328 , the left guard retaining portions  330 , and the front guard retaining portions  332  are constituted of a steel material. The container plate  320  includes a top plate  320   a  that extends in the front-rear direction and in the right-left direction and has a substantially rectangular shape with a longitudinal direction in the front-rear direction, a right flange  320   b  that is bent downward from a right end of the top plate  320   a,  a left flange  320   c  that is bent downward from a left end of the top plate  320   a,  a front flange  320   d  that is bent downward from a front end of the top plate  320   a,  and a rear flange  320   e  that is bent downward from a rear end of the top plate  320   a.  An upper surface of the top plate  320   a  configures a flat surface on which a load is to be placed. The right channel  322  and the left channel  324  extend in the front-rear direction between the front flange  320   d  and the rear flange  320   e  along a lower surface of the top plate  320   a  and are welded to the container plate  320 . The right channel  322  has a cross-sectional shape with its left side opened, and the left channel  324  has a cross-sectional shape with its right side opened. The reinforcement channels  326  extend along the lower surface of the top plate  320   a  between the right flange  320   b  and the right channel  322  and between the left flange  320   c  and the left channel  324 , and are welded to the container plate  320 . The right guard retaining portions  328  are welded to a right surface of the right flange  320   b.  The right guard retaining portions  328  are located in the vicinity of connection site of the reinforcement channels  326  and the right flange  320   b.  The left guard retaining portions  330  are welded to a left surface of the left flange  320   c.  The left guard retaining portions  330  are located in the vicinity of connection site of the reinforcement channels  326  and the left flange  320   c.  The front guard retaining portions  332  are welded to a front surface of the front flange  320   d.  The front guard retaining portions  332  are located in the vicinity of connection site of the right channel  322  and the front flange  320   d  and in the vicinity of connection site of the left channel  324  and the front flange  320   d.    
     The right guard  304  includes a guard pipe  304   a  and a support pipe  304   b.  Both of the guard pipe  304   a  and the support pipe  304   b  are constituted of a steel material. The guard pipe  304   a  extends in the front-rear direction and is bent downward at its front and rear ends. The support pipe  304   b  extends in the up-down direction and its upper end is welded to a lower surface of the guard pipe  304   a.  The left guard  306  includes a guard pipe  306   a  and a support pipe  306   b.  Both of the guard pipe  306   a  and the support pipe  306   b  are constituted of a steel material. The guard pipe  306   a  extends in the front-rear direction and is bent downward at its front and rear ends. The support pipe  306   b  extends in the up-down direction and its upper end is welded to a lower surface of the guard pipe  306   a.  The front guard  308  includes a guard pipe  308   a  and support pipes  308   b.  All of the guard pipe  308   a  and the support pipes  308   b  are constituted of a steel material. The guard pipe  308   a  extends in the right-left direction and is bent downward at its right and left ends. The support pipes  308   b  extend in the up-down direction and their upper ends are welded to a lower surface of the guard pipe  308   a.  The rear guard  310  includes a guard pipe  310   a  and a guard plate  310   b.  Both of the guard pipe  310   a  and the guard plate  310   b  are constituted of a steel material. The guard pipe  310   a  extends in the right-left direction, is bent downward at its right and left ends, and has the ends fixed to the rear flange  320   e  of the container plate  320 . The guard plate  310   b  extends in the up-down direction and the right-left direction, and has its left and right ends welded to the guard pipe  310   a.    
     As shown in  FIG. 42 , the right guard retaining portion  328  has a substantially rectangular tube shape and includes an upper opening  328   a  and a lower opening  328   b.  An inner space of the right guard retaining portion  328  is slightly larger than an outer diameter of the support pipe  304   b  of the right guard  304  in the right-left direction and is at least twice the outer diameter of the support pipe  304   b  of the right guard  304  in the front-rear direction. A support plate  328   c  extending along the front-rear direction and the right-left direction is disposed at a lower front portion of the right guard retaining portion  328 . A flange  328   d  that is bent upward is disposed at a rear end of the support plate  328   c.  A right surface of the right guard retaining portion  328  is provided with a right opening  328   e  that is continuous from the lower opening  328   b.  A retaining screw  304   c  is attached to the vicinity of lower end of the support pipe  304   b  of the right guard  304 . The retaining screw  304   c  is attached to the support pipe  304   b  through the right opening  328   e  with the support pipe  304   b  inserted in the right guard retaining portion  328  from above. The retaining screw  304   c  engages with an edge of the right opening  328   e  when the support pipe  304   b  is moved upward relative to the right guard retaining portion  328  to prevent the support pipe  304   b  from getting out from the right guard retaining portion  328 . An inner surface of the right guard retaining portion  328  is provided with a rubber  328   f  for suppressing damage due to contact with the support pipe  304   b.    
     When the lower end of the support pipe  304   b  is in contact with the support plate  328   c  as shown in  FIG. 42 , the right guard  304  is retained by the right guard retaining portion  328  such that the upper end of the guard pipe  304   a  is positioned higher than the upper surface of the top plate  320   a  as shown in  FIG. 39 . In this state, the right guard  304  can prevent a load placed on the container plate  320  from falling off from the right side. The state of the right guard  304  shown in  FIG. 42  may be referred to as a first state. 
     When the right guard  304  is lifted upward, moved rearward, and then moved downward in the first state of  FIG. 42 , the support pipe  304   b  penetrates through the right guard retaining portion  328  and the lower surface of the guard pipe  304   a  makes contact with an edge of the upper opening  328   a  of the right guard retaining portion  328  as shown in  FIG. 43 . In this case, as shown in  FIG. 44 , the right guard  304  is retained by the right guard retaining portion  328  such that the upper end of the guard pipe  304   a  is positioned lower than the upper surface of the top plate  302   a.  In this state, the right guard  304  does not interrupt loading and unloading of a load onto/from the container plate  320 , which improves loading/unloading efficiency. The state of the right guard  304  shown in  FIG. 43  may be referred to as a second state. When the right guard  304  is lifted upward, moved forward, and then moved downward in the second state of  FIG. 43 , the right guard  304  is brought back to the first state shown in  FIG. 42 . In the first container unit  300  of the present embodiment, the right guard  304  is not brought from the first state of  FIG. 42  to the second state of  FIG. 43  unintentionally because the flange  328   d  is disposed at the rear end of the support plate  328   c.    
     In the present embodiment, the height of the right guard  304  relative to the container plate  320  can be changed by moving the right guard  304  in the up-down direction and front-rear direction, without moving it in the right-left direction. For example, in a top plan view of the first container unit  300  with the first state of  FIG. 42 , an interval between the right guard  304  and the container plate  320  is 30 mm±5 mm, and in a top plan view of the first container unit  300  with the second state of  FIG. 43 , an interval between the right guard  304  and the container plate  320  is 30 mm±5 mm. In the top view of the first container unit  300 , change in the interval between the right guard  304  and the container plate  320  when the right guard  304  is brought from the first state of  FIG. 42  to the second state of  FIG. 43  and when the right guard  304  is brought from the second state of  FIG. 43  to the first state of  FIG. 42  is within a range of ±5 mm. This configuration enables height change of the right guard  304  relative to the container plate  320  even in a situation where a wide working space in the right-left direction cannot be secured. In the first state of  FIG. 42  and the second state of  FIG. 43 , an interval into which the user can insert his/her finger(s) is left between the right guard  304  and the container plate  320 , thus the user can easily grip the right guard  304 . 
     Further, in the present embodiment, the height of the right guard  304  relative to the container plate  320  can be changed without substantially changing the angle of the right guard  304  relative to the container plate  320 . For example, the angle of the right guard  304  relative to the container plate  320  is 90 degrees±3 degrees in the first state shown in  FIG. 42 , and the angle of the right guard  304  relative to the container plate  320  is 90 degrees±3 degrees in the second state shown in  FIG. 43 . Further, change in the angle of the right guard  304  relative to the container plate  320  when the right guard  304  transitions from the first state of  FIG. 42  to the second state of  FIG. 43  and when the right guard  304  transitions from the second state of  FIG. 43  to the first state of  FIG. 42  is within a range of ±3 degrees. This configuration enables height change of the right guard  304  relative to the container plate  320  even in a situation where a wide working space in the right-left direction cannot be secured. 
     The left guard retaining portion  330  has a configuration similar to that of the right guard retaining portion  328 . In the state shown in  FIG. 39 , the left guard  306  is retained by the left guard retaining portion  330  such that an upper end of the guard pipe  306   a  is positioned higher than the upper surface of the top plate  320   a.  When the left guard  306  is lifted upward, moved rearward, and then moved downward in this state, the left guard  306  is retained by the left guard retaining portion  330  such that the upper end of the guard pipe  306   a  is positioned lower than the upper surface of the top plate  302   a,  as shown in  FIG. 44 . When the left guard  306  is lifted upward, moved forward, and then moved downward in the state of  FIG. 44 , the left guard  306  is brought back to the state of  FIG. 39 . 
     The front guard retaining portion  332  also has a similar configuration to that of the right guard retaining portion  328 . In the state shown in  FIG. 39 , the front guard  308  is retained by the front guard retaining portion  332  such that an upper end of the guard pipe  308   a  is positioned higher than the upper surface of the top plate  320   a.  When the front guard  308  is lifted upward, moved leftward, and then moved downward in this state, the front guard  308  is retained by the front guard retaining portion  332  such that the upper end of the guard pipe  308   a  is positioned lower than the upper surface of the top plate  302   a,  as shown in  FIG. 44 . When the front guard  308  is lifted upward, moved rightward, and then moved downward in the state of  FIG. 44 , the front guard  308  is brought back to the state of  FIG. 39 . 
     As shown in  FIG. 41 , the support base  318  includes a right channel  334 , a left channel  336 , a front plate  338 , a rear plate  340 , and a reinforcement frame  342 . All of the right channel  334 , the left channel  336 , the front plate  338 , the rear plate  340 , the reinforcement frame  342  are constituted of a steel material. The right channel  334  and the left channel  336  extend in the front-rear direction. The right channel  334  has a cross-sectional shape with its left side opened, and the left channel  336  has a cross-sectional shape with its right side opened. The front plate  338  is welded to a front end of the right channel  334  and a front end of the left channel  336 . The rear plate  340  is welded to a rear end of the right channel  334  and a rear end of the left channel  336 . As shown in  FIG. 40 , the first container unit  300  is fixed to the chassis unit  4  by screwing the front plate  338  to the right bracket  164  and the left bracket  170  of the front wheel unit  12  and also screwing the rear plate  340  to the frame plate  130  of the chassis frame  10 . The reinforcement frame  342  extends in the right-left direction, a right end thereof is welded to the right channel  334 , and a left end thereof is welded to the left channel  336 . 
     As shown in  FIG. 41 , the first arms  312  and the second arms  314  are connected to each other to be pivotable about a pivot axis, which is the right-left direction. The first arms  312  and the second arms  314  are both constituted of a steel material. Lower ends of the first arms  312  are supported at the vicinity of the front end of the right channel  334  and at the vicinity of the front end of the left channel  336  of the support base  318  such that they are pivotable about a pivot axis, which is the right-left direction. Upper ends of the first arms  312  include rollers  312   a  and  312   b,  respectively. The rollers  312   a  and  312   b  are supported by the right channel  322  and left channel  324  of the container  302 , respectively. Upper ends of the second arms  314  are supported at the vicinity of the front end of the container plate  320  of the container  302  such that they are pivotable about a pivot axis, which is the right-left direction. Lower ends of the second arms  314  include rollers  314   a  and  314   b  (see  FIG. 40 ), respectively. The rollers  314   a  and  314   b  are supported by the right channel  334  and the left channel  336  of the support base  318 , respectively. A reinforcement frame  344  is welded to the first arms  312 . 
     The actuator  316  is a linear actuator configured to contract and expand, for example, a hydraulic cylinder. One end of the actuator  316  is supported by the reinforcement frame  342  of the support base  318  to be pivotable about a pivot axis, which is the right-left direction. 
     Another end of the actuator  316  is supported by the reinforcement frame  344  of the first arms  312  to be pivotable about a pivot axis, which is the right-left direction. The actuator  316  is connected to the battery box  8  via a power cable (not shown). The actuator  316  is supplied with the power from the battery packs  112 . Operation of the actuator  316  is controlled by the control board  108 . When the actuator  316  contracts, the first arms  312  are pivoted in a direction that brings the upper ends of the first arms  312  close to the support base  318  and the second arms  314  are also pivoted in a direction that brings the lower ends of the second arms  314  close to the container  302 , as a result of which the container  302  is lowered to the support base  318  as shown in  FIG. 39 . When the actuator  316  expands, the first arms  312  are pivoted in a direction that brings the upper ends of the first arms  312  away from the support base  318  and the second arms  314  are also pivoted in a direction that brings the lower ends of the second arms  314  away from the container  302 , as a result of which the container  302  is lifted relative to the support base  318  as shown in  FIG. 40 . The control board  108  controls the actuator  316  to expand while the user presses an upper portion of the container operation switch  120   e.  The control board  108  controls the actuator  316  to contract while the user presses a lower portion of the container operation switch  120   e.    
     (Second Container Unit  400 ) 
     As shown in  FIGS. 45, 46, and 47 , the second container unit  400  includes a bucket  402 , a bucket support base  404 , support arms  406 , a movable support base  408 , an actuator  410 , and a fixed support base  412 . The fixed support base  412  of the second container unit  400  is screwed and fixed to the chassis frame  10 . The second container unit  400  is configured to tilt the movable support base  408  relative to the fixed support base  412  by the actuator  410  as shown in  FIG. 46 . Further, the second container unit  400  is configured to further tilt the bucket  402  relative to the fixed support base  412  as shown in  FIG. 47  by the user tilting the bucket support base  404  relative to the movable support base  408 . 
     The bucket  402  has a box shape with its upper side open. As shown in  FIG. 48 , the bucket support base  404  includes a base plate  416 , a base pipe  418 , an upper frame  420 , a lower frame  422 , a handle  424 , and a latch mechanism  426 . All of the base plate  416 , the base pipe  418 , the upper frame  420 , and the lower frame  422  are constituted of a steel material. The base plate  416  is disposed along the front-rear direction and the right-left direction. The base pipe  418  extends along a lower surface of a front lower portion of the bucket  402  and also extends in the front-rear direction along a lower surface of the base plate  416 . The base pipe  418  is screwed to the front lower portion of the bucket  402  and is also screwed to the base plate  416 . The upper frame  420  is disposed between a lower surface of a rear lower portion of the bucket  402  and the upper surface of the base plate  416 , along the front-rear direction and the up-down direction. The upper frame  420  is screwed to the rear lower portion of the bucket  402  and is also screwed to the base plate  416 . The lower frame  422  extends in the front-rear direction along the lower surface of the base plate  416 . The lower frame  422  is welded to the base plate  416 . The handle  424  is disposed rearward of the bucket  402 . The handle  424  is screwed to the lower frame  422 . The latch mechanism  426  is disposed below the handle  424 . The latch mechanism  426  is fixed to the base plate  416  and the lower frame  422 . 
     The movable support base  408  includes a right frame  428 , a left frame  430 , a front frame  432 , a rear frame  434 , and a latch receiver  436 . All of the right frame  428 , the left frame  430 , the front frame  432 , and the rear frame  434  are constituted of a steel material. The right frame  428  and the left frame  430  extend in the front-rear direction. A front end of the right frame  428  and a front end of the left frame  430  are connected to a front end of the lower frame  422  of the bucket support base  404  to be pivotable about a pivot axis, which is the right-left direction. The front frame  432  extends in the right-left direction between the vicinity of the front end of the right frame  428  and the vicinity of the front end of the left frame  430 . The front frame  432  is welded to the right frame  428  and the left frame  430 . The rear frame  434  extends in the right-left direction between a rear end of the right frame  428  and a rear end of the left frame  430 . The rear frame  434  is welded to the right frame  428  and the left frame  430 . The latch receiver  436  is fixed at the vicinity of a center of the rear frame  434 . The latch receiver  436  is disposed at a position corresponding to the latch mechanism  426  of the bucket support base  404 . When the bucket support base  404  is tilted relative to the movable support base  408  in a direction that brings a rear end of the bucket support base  404  close to a rear end of the movable support base  408 , the latch mechanism  426  engages with the latch receiver  436 . The latch mechanism  426  includes a unlatch knob  426   a.  The latch mechanism  426  is disengaged from the latch receiver  436  by the user operating the unlatch knob  426   a  when the latch mechanism  426  is engaged with the latch receiver  436 . 
     The fixed support base  412  includes a right channel  438 , a left channel  440 , a front plate  442 , a rear plate  444 , and a reinforcement frame  446 . All of the right channel  438 , the left channel  440 , the front plate  442 , the rear plate  444 , and the reinforcement frame  446  are constituted of a steel material. The right channel  438  and the left channel  440  extend in the front-rear direction. The right channel  438  has a cross-sectional shape with its left side opened, and the left channel  440  has a cross-sectional shape with its right side opened. The front plate  442  is welded to a front end of the right channel  438  and a front end of the left channel  440 . The rear plate  444  is welded to a rear end of the right channel  438  and a rear end of the left channel  440 . As shown in  FIGS. 46 and 47 , the second container unit  400  is fixed to the chassis unit  4  by screwing the front plate  442  to the right bracket  164  and the left bracket  170  of the front wheel unit  12  and also screwing the rear plate  444  to the frame plate  130  of the chassis frame  10 . The reinforcement frame  446  extends in the right-left direction, a right end thereof is welded to the right channel  438 , a left end thereof is welded to the left channel  440 . 
     As shown in  FIG. 48 , upper ends of the support arms  406  are connected to the vicinity of the front end of the lower frame  422  of the bucket support base  404  to be pivotable about a pivot axis, which is the right-left direction. The support arms  406  are constituted of a steel material. Lower ends of the support arms  406  include rollers  406   a  and  406   b,  respectively. The rollers  406   a  and  406   b  are supported by the right channel  438  and left channel  440  of the fixed support base  412 , respectively. 
     The actuator  410  is a linear actuator configured to contract and expand, for example a hydraulic cylinder. One end of the actuator  410  is supported by the reinforcement frame  446  of the fixed support base  412  to be pivotable about a pivot axis, which is the right-left direction. Another end of the actuator  410  is supported by the front frame  432  of the movable support base  408  to be pivotable about a pivot axis in the right-left direction. The actuator  410  is connected to the battery box  8  of the chassis unit  4  via a power cable (not shown). The actuator  410  is supplied with the power from the battery packs  112 . Operation of the actuator  410  is controlled by the control board  108 . When the actuator  410  contracts, the movable support base  408  is pivoted relative to the fixed support base  412  in a direction that brings the rear end of the movable support base  408  close to the rear end of the fixed support base  412 , as a result of which the movable support base  408  and the bucket support base  404  become substantially parallel to the fixed support base  412  as shown in  FIG. 45 . When the actuator  410  expands, the movable support base  408  is pivoted relative to the fixed support base  412  in a direction that brings the rear end of the movable support base  408  away from the rear end of the fixed support base  412 , as a result of which the movable support base  408  and the bucket support base  404  become tilted relative to the fixed support base  412  as shown in  FIG. 46 . The control board  108  controls the actuator  410  to expand while the user presses the upper portion of the container operation switch  120   e.  The control board  108  controls the actuator  410  to contract while the user presses the lower portion of the container operation switch  120   e.  When the user operates the unlatch knob  426   a  to disengage the latch mechanism  426  from the latch receiver  436  in the state shown in  FIG. 46  and further pivots the handle  424  forward, the bucket support base  404  becomes tilted relative to the movable support base  408  as shown in  FIG. 47 . 
     (Third Container Unit  500 ) 
     As shown in  FIGS. 49 and 50 , the third container unit  500  includes a bucket  502 , a movable support base  504 , support arms  506 , and a fixed support base  508 . The fixed support base  508  of the third container unit  500  is screwed and fixed to the chassis unit  4 . The third container unit  500  is configured to tilt the bucket  502  relative to the fixed support base  508  as shown in  FIG. 50  by the user tilting the movable support base  504  relative to the fixed support base  508 . 
     The bucket  502  has a box shape with its upper side opened. As shown in  FIG. 51 , the movable support base  504  includes a base plate  510 , a base pipe  512 , an upper frame  514 , a lower frame  516 , a handle  518 , and a latch mechanism  520 . All of the base plate  510 , the base pipe  512 , the upper frame  514 , and the lower frame  516  are constituted of a steel material. The base plate  510  is disposed along the front-rear direction and the right-left direction. The base pipe  512  extends along a lower surface of a front lower portion of the bucket  502  and also extends in the front-rear direction along a lower surface of the base plate  510 . The base pipe  512  is screwed to the front lower portion of the bucket  502  and is also screwed to the base plate  510 . The upper frame  514  is disposed between a lower surface of a rear lower portion of the bucket  502  and an upper surface of the base plate  510 , along the front-rear direction and the up-down direction. The upper frame  514  is screwed to the rear lower portion of the bucket  502  and is also screwed to the base plate  510 . The lower frame  516  extends in the front-rear direction along the lower surface of the base plate  510 . The lower frame  516  is welded to the base plate  510 . The handle  518  is located rearward of the bucket  502 . The handle  518  is screwed to the lower frame  516 . The latch mechanism  520  is disposed below the handle  518 . The latch mechanism  520  is fixed to the base plate  510  and the lower frame  516 . 
     The fixed support base  508  includes a right channel  522 , a left channel  524 , a front plate  526 , a rear plate  528 , a reinforcement frame  530 , and a latch receiver  532 . All of the right channel  522 , the left channel  524 , the front plate  526 , the rear plate  528 , and the reinforcement frame  530  are constituted of a steel material. The right channel  522  and the left channel  524  extend in the front-rear direction. The right channel  522  has a cross-sectional shape with its left side opened, and the left channel  524  has a cross-sectional shape with its right side opened. The front plate  526  is welded to a front end of the right channel  522  and a front end of the left channel  524 . The rear plate  528  is welded to a rear end of the right channel  522  and a rear end of the left channel  524 . As shown in  FIGS. 49 and 50 , the third container unit  500  is fixed to the chassis unit  4  by screwing the front plate  526  to the right bracket  164  and the left bracket  170  of the front wheel unit  12  and also screwing the rear plate  528  to the frame plate  130  of the chassis frame  10 . As shown in  FIG. 51 , the reinforcement frame  530  extends in the right-left direction, a right end thereof is welded to the right channel  522 , and a left end thereof is welded to the left channel  524 . The latch receiver  532  is fixed at the vicinity of a center of the rear plate  528 . The latch receiver  532  is disposed at a position corresponding to the latch mechanism  520  of the movable support base  504 . When the movable support base  504  is tilted relative to the fixed support base  508  in a direction that brings a rear end of the movable support base  504  close to a rear end of the fixed support base  508 , the latch mechanism  520  engages with the latch receiver  532 . The latch mechanism  520  includes an unlatch knob  520   a.  The latch mechanism  520  is disengaged from the latch receiver  532  by the user operating the unlatch knob  520   a  when the latch mechanism  520  is engaged with the latch receiver  532 . 
     Upper ends of the support arms  506  are connected to the vicinity of a front end of the lower frame  516  of the movable support base  504  to be pivotable about a pivot axis, which is the right-left direction. The support arms  506  are constituted of a steel material. Lower ends of the support arms  506  include rollers  506   a  and  506   b,  respectively. The rollers  506   a  and  506   b  are supported by the right channel  522  and the left channel  524  of the fixed support base  508 , respectively. 
     When the user operates the unlatch knob  520   a  to disengage the latch mechanism  520  from the latch receiver  532  in the state shown in  FIG. 49  and further pivots the handle  518  in forward, the movable support base  504  becomes tilted relative to the fixed support base  508  as shown in  FIG. 50 . 
     (Fourth Container Unit  600 ) 
     As shown in  FIGS. 52 and 53 , the fourth container unit  600  includes a container  602 , a movable support base  604 , a support arm (not shown), and a fixed support base  606 . The fixed support base  606  of the fourth container unit  600  is screwed and fixed to the chassis unit  4 . The fourth container unit  600  is configured to tilt the container  602  relative to the fixed support base  606  by the user tilting the movable support base  604  relative to the fixed support base  606 . 
     The container  602  includes a main frame  608 , a right guard  610 , a left guard  612 , and a front guard  614 . The main frame  608  includes a frame pipe  616 , a floor pipe  618 , a reinforcement pipe  620 , a right guard retaining pipe  622 , a left guard retaining pipe  624 , and a front guard retaining pipe  626 . All of the frame pipe  616 , the floor pipe  618 , the reinforcement pipe  620 , the right guard retaining pipe  622 , the left guard retaining pipe  624 , and the front guard retaining pipe  626  are constituted of a steel material. The frame pipe  616  forms a substantially rectangular shape of which longitudinal direction is along the front-rear direction and short direction is along the right-left direction. The floor pipe  618  extends in the front-rear direction on substantially the same plane as the frame pipe  616 , and front and rear ends thereof are welded to the frame pipe  616 . The reinforcement pipe  620  extends in the right-left direction along lower surfaces of the frame pipe  616  and the floor pipe  618  and is welded to the frame pipe  616  and the floor pipe  618 . The right guard retaining pipe  622  is disposed in the vicinity of a right end of the main frame  608 , extends in the right-left direction along the lower surfaces of the frame pipe  616  and the floor pipe  618 , and is welded to the frame pipe  616  and the floor pipe  618 . The left guard retaining pipe  624  is disposed in the vicinity of a left end of the main frame  608 , extends in the right-left direction along the lower surfaces of the frame pipe  616  and the floor pipe  618 , and is welded to the frame pipe  616  and the floor pipe  618 . The front guard retaining pipe  626  is disposed in the vicinity of a front end of the main frame  608 , extends in the front-rear direction along the lower surface of the floor pipe  618 , and is welded to the floor pipe  618 . A hook  616   a  projecting downward is disposed on the lower surface of the frame pipe  616 . When roping a load placed on the container  602 , the user can hook the rope on the hook  616   a.    
     The right guard  610  includes a guard pipe  628  and an insertion pipe  630 . The guard pipe  628  and the insertion pipe  630  are both constituted of a steel material. The guard pipe  628  forms a substantially rectangular shape of which longitudinal direction is along the front-rear direction and short direction is along the up-down direction. The insertion pipe  630  extends in the right-left direction and a right end thereof is welded to a lower portion of the guard pipe  628 . Insertion of the insertion pipe  630  into the right guard retaining pipe  622  enables the right guard  610  to be retained by the main frame  608 . The right guard retaining pipe  622  includes a grip bolt  622   a  for fixing the position of the insertion pipe  630  to the right guard retaining pipe  622 . 
     The user adjusts the position of the right guard  610  to the main frame  608  in the right-left direction with the grip bolt  622   a  loosened and then tightens the grip bolt  622   a  to fix the right guard  610  at a desired position to the main frame  608 . 
     The left guard  612  includes a guard pipe  632  and an insertion pipe  634 . The guard pipe  632  and the insertion pipe  634  are both constituted of a steel material. The guard pipe  632  forms a substantially rectangular shape of which longitudinal direction is along the front-rear direction and short direction is along the up-down direction. The insertion pipe  634  extends in the right-left direction and a left end thereof is welded to a lower portion of the guard pipe  632 . Insertion of the insertion pipe  634  into the left guard retaining pipe  624  enables the left guard  612  to be retained by the main frame  608 . The left guard retaining pipe  624  includes a grip bolt  624   a  for fixing the position of the insertion pipe  634  to the left guard retaining pipe  624 . The user adjusts the position of the left guard  612  to the main frame  608  in the right-left direction with the grip bolt  624   a  loosened and then tightens the grip bolt  624   a  to fix the left guard  612  at a desired position to the main frame  608 . 
     The front guard  614  includes a guard pipe  636  and an insertion pipe  638 . The guard pipe  636  and the insertion pipe  638  are both constituted of a steel material. The guard pipe  636  forms a substantially rectangular shape of which longitudinal direction is along the right-left direction and short direction is along the up-down direction. The insertion pipe  638  extends in the front-rear direction and a front end thereof is welded to a lower portion of the guard pipe  636 . Insertion of the insertion pipe  638  into the front guard retaining pipe  626  enables the front guard  614  to be retained by the main frame  608 . The front guard retaining pipe  626  includes a grip bolt  626   a  for fixing the position of the insertion pipe  638  to the front guard retaining pipe  626 . The user adjusts the position of the front guard  614  to the main frame  608  in the front-rear direction with the grip bolt  626   a  loosened and then tightens the grip bolt  626   a  to fix the front guard  614  at a desired position to the main frame  608 . 
     The movable support base  604  includes a base plate  640 , a lower frame  642 , a handle  644 , and a latch mechanism  646 . The configurations of the base plate  640 , the lower frame  642 , the handle  644 , and the latch mechanism  646  are similar to those of the base plate  510 , the lower frame  516 , the handle  518 , and the latch mechanism  520  of the third container unit  500 . The reinforcement pipe  620  of the main frame  608  is screwed to the base plate  640 . 
     The fixed support base  606  includes a right channel  648 , a left channel  650 , a front plate  652 , a rear plate  654 , a reinforcement frame  656 , and a latch receiver  658 . The configuration of the fixed support base  606  is similar to that of the fixed support base  508  of the third container unit  500 . Further, how the movable support base  604  is connected to the fixed support base  606  is similar to how the movable support base  504  is connected to the fixed support base  508  in the third container unit  500 . That is, most of the components of the fourth container unit  600  are common with the components of the third container unit  500 . Similar to the third container unit  500 , when the user operates the unlatch knob  646   a  to disengage the latch mechanism  646  from the latch receiver  658  in the state shown in  FIG. 52  and further pivots the handle  644  forward, the movable support base  604  becomes tilted relative to the fixed support base  606  in the fourth container unit  600 . 
     (Fifth Container Unit  700 ) 
     As shown in  FIGS. 54 and 55 , the fifth container unit  700  includes a bucket  702  and a support base  704 . The support base  704  of the fifth container unit  700  is screwed and fixed to the chassis unit  4 . In the fifth container unit  700 , the bucket  702  is not fixed to the support base  704 , thus the user can lift the bucket  702  to remove it from the support base  704  and place the bucket  702  onto the support base  704 . 
     As shown in  FIG. 54 , the bucket  702  has a box shape with its upper side opened. A through hole  702   a  is disposed in a lower portion of a front surface of the bucket  702 . A cap  706  is detachably attached to the through hole  702   a.    
     As shown in  FIG. 55 , the support base  704  includes a central frame  708 , a right channel  710 , a left channel  712 , a front plate  714 , a rear plate  716 , a right guard  718 , and a left guard  720 . All of the central frame  708 , the right channel  710 , the left channel  712 , the front plate  714 , and the rear plate  716  are constituted of a steel material. The central frame  708 , the right channel  710 , and the left channel  712  extend along the front-rear direction. The front plate  714  is welded to a front end of the central frame  708 , a front end of the right channel  710 , and a front end of the left channel  712 . The rear plate  716  is welded to a rear end of the central frame  708 , a rear end of the right channel  710 , and a rear end of the left channel  712 . As shown in  FIG. 54 , the fifth container unit  700  is fixed to the chassis unit  4  by screwing the front plate  714  to the right bracket  164  and the left bracket  170  of the front wheel unit  12  and screwing the rear plate  716  to the frame plate  130  of the chassis frame  10 . 
     The right guard  718  includes a guard pipe  722  and a reinforcement pipe  724 . The guard pipe  722  and the reinforcement pipe  724  are both constituted of a steel material. The guard pipe  722  extends in the front-rear direction along a right surface of the bucket  702 . The guard pipe  722  is bent downward and leftward at a front end of the bucket  702  along a front surface of the bucket  702  and is connected to the front plate  714 . The guard pipe  722  is also bent downward and leftward at a rear end of the bucket  702  along a rear surface of the bucket  702  and is connected to the rear plate  716 . The reinforcement pipe  724  connects between the guard pipe  722  and the right channel  710 . 
     As shown in  FIG. 55 , the left guard  720  includes a guard pipe  726  and a reinforcement pipe  728 . The guard pipe  726  and the reinforcement pipe  728  are both constituted of a steel material. The guard pipe  726  extends in the front-rear direction along a left surface of the bucket  702 . The guard pipe  726  is bent downward and rightward at the front end of the bucket  702  along the front surface of the bucket  702  and is connected to the front plate  714 . The guard pipe  726  is also bent downward and rightward at the rear end of the bucket  702  along the rear surface of the bucket  702  and is connected to the rear plate  716 . The reinforcement pipe  728  connects between the guard pipe  722  and the left channel  712 . 
     As described, in one or more embodiments, the cart  2  (an example of handcart) comprises the right front wheel  140  and the left front wheel  142  (examples of drive wheel); the motor  150  (an example of prime mover) configured to rotate the right front wheel  140  and the left front wheel  142 ; the right handle  18  and the left handle  20  (examples of grip portion) configured to be gripped by the user; and the taillight  74  (an example of visibly noticeable portion) that is clearly noticeable from behind the user when the user stands behind the cart  2 , gripping the right handle  18  and the left handle  20 . 
     In this configuration, the taillight  74  can be visually noticed from behind the user even when the user stands behind the cart  2 , gripping the right handle  18  and the left handle  20 . Thus, the configuration can inform a person or a car coming from behind that transferring work is in progress with the cart  2 . 
     In one or more embodiments, the taillight  74  configured to emit light functions as a visibly noticeable portion that is clearly noticeable. 
     This configuration can surely inform a person or a car coming from behind that transferring work is in progress with the cart  2 , even when the cart  2  is used outdoor at night and/or in bad weather or the cart  2  is used indoor, for example, in a factory. 
     In one or more embodiments, the right handle  18  includes the grip  38  extending in the front-rear direction. The taillight  74  is disposed forward of the rear end of the grip  38 . 
     In this configuration, when an object collides with the cart  2  from behind it, the object collides with the rear end of the grip  38  before reaching the taillight  74 . Thus, damage to the taillight  74  can be prevented. 
     In one or more embodiments, the cart  2  further comprises the casing  66  disposed near the grip  38  and the operation lever  72  (an example of operation member) supported by the casing  66  and configured to be operable by the user with the user gripping the grip  38 . The motor  150  is configured to rotate the right front wheel  140  and the left front wheel  142  when the operation lever  72  is operated by the user. 
     This configuration enables the user to perform an operation for driving the motor  150  while the user grips the grip  38 , thus it improves convenience for the user. 
     In one or more embodiments, the taillight  74  is disposed on the rear surface of the casing  66 . 
     This configuration can simplify the configuration of the cart  2  as compared to a configuration in which the taillight  74  is disposed separately from the casing  66  which supports the operation lever  72 . 
     In one or more embodiments, the cart  2  further comprises the alarm sound button  70  supported by the casing  66  and configured to be operable by the user with the user gripping the grip  38 ; and the buzzer  124  (an example of alarm sound emitter) configured to emit the alarm sound when the alarm sound button  70  is operated by the user. 
     This configuration can inform a person or a car that is present in other directions than behind the cart  2  that transferring work is in progress with the cart  2 , by emitting the alarm sound from the buzzer  124 . Further, the configuration enables the user to perform an operation for emitting the alarm sound from the buzzer  124  while the user grips the grip  38 , thus it can improve the user&#39;s convenience. 
     In one or more embodiments, the motor  150  functions as a prime mover configured to rotate the right front wheel  140  and the left front wheel  142 . 
     This configuration can suppress vibrations transmitted to a load on the cart  2  as compared to a configuration in which an engine is used as the prime mover for rotating the right front wheel  140  and the left front wheel  142 . 
     In one or more embodiments, the cart  2  further comprises the battery mounting portions  110  to which the battery packs  112  are detachably attached. The motor  150  is driven by electric power from the battery packs  112 . 
     This configuration enables the motor  150  to be supplied with the electric power, without connecting the cart  2  with an external power supply via a power cord.