Patent Publication Number: US-2022233373-A1

Title: Wheelchair

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2021-011284 filed on Jan. 27, 2021, the entire disclosure of which is incorporated by reference herein. 
     BACKGROUND 
     The present disclosure relates to a foldable wheelchair configured to be foldable. 
     Foldable wheelchairs configured to be foldable when not in use have been traditionally known (e.g., see Japanese Unexamined Patent Publication No. 2016-198334). The wheelchair of Japanese Unexamined Patent Publication No. 2016-198334 includes left- and right-side frames that pivotably support driving wheels, and a support arm and a cross member that connect the left- and right-side frames. At a time of using the wheelchair, the support arm and the cross member are swung in directions to spread the distance between the left- and right-side frames so as to make the support arm and the cross member in an unfolded state. On the other hand, when the wheelchair is not used, arm supports of the left- and right-side frames are held and a force is applied in directions to narrow the distance between the left- and right-side frames so as to swing the support arm and the cross member to a folded state. 
     SUMMARY 
     As in the wheelchair of Japanese Unexamined Patent Publication No. 2016-198334, by folding the wheelchair and make it compact while not in use, the space required for storage of the wheelchair can be small. For this reason, foldable wheelchairs are widely used. 
     Meanwhile, there is a case of lifting and move the wheelchair by one hand after folding the wheelchair body. Wheelchairs in general are not expected to be lifted by one hand in the first place. Therefore, in such a case, it is hard to find where to hold. Even if the wheelchair is held by one hand, the wheelchair that is not expected to be held by one hand is likely to become unstable and is likely to end up being inclined with its front part lower than its rear part. Since the wheelchair has pivotable casters (front wheels) in its front part, the casters hang down and contacts the ground when the front part of the wheelchair is lowered. For this reason, the wheelchair needs to be lifted to a higher position. 
     Further, in cases of a wheelchair user capable of driving a motor vehicle, the wheelchair user may drive the motor vehicle alone to expand the freedom of his/her activities. In this case, the wheelchair user needs to move the wheelchair outside the motor vehicle to the inside after the wheelchair user has moved from the wheelchair to the driver seat of the motor vehicle. At this time, it is difficult to lift the wheelchair with both hands, and there is no choice but to lift the wheelchair by one hand. Doing so, however, causes the casters to hand down and contact the lower edge part of the door opening, causing difficulty to stow the wheelchair inside. It is therefore necessary to lift the wheelchair to a higher position, which is a significant burden for the wheelchair user. 
     In view of the above points, an object of the present disclosure is to make it easier to lift and move a wheelchair by keeping casters from hanging even when the wheelchair is lifted by one hand. 
     To achieve the above object, a first aspect of the present disclosure premises a foldable wheelchair that allows a wheelchair user to sit thereon. The wheelchair includes: a left-side frame that pivotably supports a rear drive wheel on a left side of a vehicle body, and has a caster attached pivotably about a center line extended in an upward-downward direction, at a part distanced from the rear drive wheel towards a front of the vehicle body; a right-side frame that pivotably supports a rear drive wheel on a right side of the vehicle body, and has a caster attached pivotably about a center line extended in the upward-downward direction, at a part distanced from the rear drive wheel towards the front of the vehicle body; a left-side support arm pivotably coupled to the left-side frame; a right-side support arm pivotably coupled to the right-side frame; a folding mechanism coupling the left-side support arm and the right-side support arm in a foldable manner in a left-right direction of the vehicle body. The folding mechanism includes an operation part for use in changing a state of the left-side support arm and the right-side support arm from one of a folded state or an unfolded state to another. The operation part is arranged between the rear drive wheel and the caster in a side view of the vehicle body. 
     According to the configuration, the left-side support arm and the right-side support arm can be easily changed from the unfolded state to the folded state, or from the folded state to the unfolded state by operating the operation part. Therefore, for example, a wheelchair user can fold the wheelchair to make it compact or unfold the wheelchair so that he/she can sit thereon, while the wheelchair user sits on a driver seat or a passenger seat of a motor vehicle. 
     The wheelchair can be lifted by holding the operation part with one hand after the wheelchair is folded. Here, the center of gravity of a wheelchair in general is positioned in the vicinity of the rear wheels. Therefore, holding the operation part between the rear wheel and the caster in a side view of the vehicle body after the wheelchair is folded causes the rear part of the wheelchair body to be in a position lower than the front part thereof. Therefore, the casters are kept from hanging down, and are less likely to contact the lower edge of the opening of the door, in a case of, for example, moving the wheelchair from outside the motor vehicle to the inside. 
     In a second aspect of the present disclosure, the left-side support arm includes a first left-side support arm and a second left-side support arm arranged on the rear side of the vehicle body relative to the first left-side support arm, and the right-side support arm includes a first right-side support arm and a second right-side support arm arranged on the rear side of the vehicle body relative to the first right-side support arm. The folding mechanism foldably couples the first left-side support arm and the first right-side support arm, while foldably coupling the second left-side support arm and the second right-side support arm. The operation part is arranged above the first left-side support arm and the first right-side support arm and is for operating the first left-side support arm and the first right-side support arm. 
     According to the configuration, the first left-side support arm and the first right-side support arm couples the left-side frame and the right-side frame. Further, the second left-side support arm and the second right-side support arm couples the left-side frame and the right-side frame. Therefore, the left-side frame and the right-side frame are coupled at least at two positions apart from each other in the front-rear direction. This strengthens the wheelchair body. In this case, a part of the wheelchair forward to the center of gravity thereof can be lifted by arranging the operation part above the first left-side support arm and the first right-side support arm positioned relatively front. Therefore, the casters are kept from hanging down. 
     In a third aspect of the present disclosure, the folding mechanism includes an interlocking member that couples, in an interlocking manner, the first left-side support arm and the first right-side support arm with the second left-side support arm and the second right-side support arm. 
     According to the configuration, the first left-side support arm and the first right-side support arm can be folded or unfolded by operating the operation part. Here, the first left-side support arm and the first right-side support arm are coupled with the second left-side support arm and the second right-side support arm via the interlocking member. Therefore, the first left-side support arm and the first right-side support arm can be interlocked with the second left-side support arm and the second right-side support arm via the interlocking member. Thus, simply operating a single operation part allows folding and unfolding of the first left-side support arm and the first right-side support arm, as well as the second left-side support arm and the second right-side support arm. 
     In a fourth aspect of the present disclosure, the first left-side support arm and the first right-side support arm are in a position higher than the second left-side support arm and the second right-side support arm. 
     According to the configuration, the positions of the first left-side support arm and the first right-side support arm are relatively high, and therefore the operation part arranged above the first left-side support arm and the first right-side support arm are also positioned at a relatively high position. This makes it easier for the wheelchair user to hold the operation part. 
     A fifth aspect of the present disclosure includes a seat frame that supports a seat cushion part, on which a wheelchair user is to be seated, and is configured to be attachable to and detachable from the left-side frame and the right-side frame. The operation part is positioned on the front of the vehicle body relative to a center of gravity of the wheelchair body while the seat frame is detached. 
     According to the configuration, the seat frame is detached from the left-side frame and the right-side frame before the wheelchair is folded, and then the wheelchair can be folded. For example, at a time of loading the wheelchair into the motor vehicle, it is possible to lift only the seat frame to bring it in the motor vehicle, and then lift only the vehicle body of the wheelchair to bring it in the motor vehicle. 
     This reduces the weight that needs to be lifted at a time when the wheelchair is loaded into a motor vehicle. Therefore, the work of loading the wheelchair is made easier. In this case, the casters provided to the wheelchair body are kept from hanging down, because the operation part is positioned on the front side of the center of gravity of the wheelchair body. 
     In a sixth aspect of the present disclosure, the folding mechanism includes a support member that supports the operation part so as to enable switching between a state of having the operation part reclined rearward of the vehicle body and a state of having the operation part raised upward, and the state of the left-side support arm and the right-side support arm is changed from the unfolded state to the folded state through an operation of switching the state of having the operation part reclined rearward of the vehicle body to the state of having the operation part raised upward. 
     According to the above configuration, when the wheelchair user having got off the wheelchair folds the unfolded wheelchair and tries to lift up the wheelchair, the wheelchair user holds the operation part to raise it and pull the wheelchair toward him/herself, so that the wheelchair user can lift the wheelchair without taking his/her hand off the operation part. That is, a series of operations from folding to lifting of the wheelchair can be smoothly done without interruption. As hereinabove described, since the operation part of the folding mechanism for folding the wheelchair is arranged between the rear wheel and the caster in a side view of the vehicle body, it is possible to avoid the casters from hanging when the wheelchair is lifted by holding the operation part. Thus, the wheelchair lifted can be easily moved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top perspective view of a wheelchair as viewed from above, according to an embodiment of the present invention. 
         FIG. 2  is a perspective view illustrating a state in which a seat is detached from a wheelchair body. 
         FIG. 3  is a perspective view of a seat frame. 
         FIG. 4  is a left side view of the wheelchair according to the embodiment of the present invention. 
         FIG. 5  is a perspective view of the folded wheelchair body as viewed from above. 
         FIG. 6  is a plan view of the wheelchair body folded. 
         FIG. 7  is a right side view of a left-side frame. 
         FIG. 8  is a plan view of the left-side frame. 
         FIG. 9  is a perspective view of a rear side of a right-side frame as viewed from the upper left side. 
         FIG. 10  is a perspective view of a front side of the right-side frame as viewed from the upper left side. 
         FIG. 11  is a plan view of support arms and a folding mechanism. 
         FIG. 12  is a perspective view of the support arms and the folding mechanism as viewed from the upper left side. 
         FIG. 13  is a plan view of a first left-side support arm. 
         FIG. 14  is a cross-sectional view taken along line XIV-XIV in  FIG. 11 . 
         FIG. 15  is an enlarged perspective view of a vicinity of an operation part of the folding mechanism as viewed from the upper right side. 
         FIG. 16  is a partial cross-sectional view illustrating a state before a seat is attached to the wheelchair body. 
         FIG. 17  is a right side view of a right-side seat frame member. 
         FIG. 18  is a view corresponding to  FIG. 16 , illustrating a state before the seat is placed on the wheelchair body and a seat back frame is erected. 
         FIG. 19  is a view corresponding to  FIG. 16 , illustrating a state in which a seat back frame is erected. 
         FIG. 20  is a view corresponding to  FIG. 16 , which relates to Variation  1  of the embodiment. 
         FIG. 21  is a view corresponding to  FIG. 18 , which relates to Variation  1  of the embodiment. 
         FIG. 22  is a view corresponding to  FIG. 19 , which relates to Variation  1  of the embodiment. 
         FIG. 23  is a view corresponding to  FIG. 16 , which relates to Variation  2  of the embodiment. 
         FIG. 24  is a view corresponding to  FIG. 18 , which relates to Variation  2  of the embodiment. 
         FIG. 25  is a view corresponding to  FIG. 19 , which relates to Variation  2  of the embodiment. 
         FIG. 26  is a view corresponding to  FIG. 16 , which relates to Variation  3  of the embodiment. 
         FIG. 27  is a view corresponding to  FIG. 19 , which relates to Variation  3  of the embodiment. 
         FIG. 28  is a view related to Variation  3 , illustrating a case where a lock is released. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention will be described in detail below with reference to the drawings. Note that the following description of preferred embodiment is only an example in nature, and is not intended to limit the scope, applications or use of the present invention. 
       FIG. 1  is a top perspective view of a wheelchair  1  as viewed from the obliquely upper front side, according to an embodiment of the present invention. As illustrated in  FIG. 2 , the wheelchair  1  can be divided into a wheelchair body  2  and a seat  3  without using tools. The seat  3  is illustrated in  FIG. 3 .  FIG. 4  is a left side view of the wheelchair  1  with the seat  3  attached thereto. The wheelchair body  2  from which the seat  3  is detached is configured to be foldable as illustrated in  FIG. 5  and  FIG. 6 , and therefore, the wheelchair  1  of the present embodiment is a foldable wheelchair. 
     Note that, while  FIG. 2  illustrates a seat cushion part  4  and a back cushion part  5  of the seat  3 ,  FIG. 1  and  FIG. 4  omits illustration of the seat cushion part  4  and the back cushion part  5 . Further,  FIG. 3  only illustrates the outline of the seat cushion part  4  and the back cushion part  5  by using virtual lines. The specific configuration of the seat  3  will be described later. 
     In the description of this embodiment, a traveling direction in which the wheelchair  1  moves forward is simply referred to as forward, and the front of the wheelchair  1  corresponds to the front of a wheelchair user (not shown) seated on the wheelchair  1 . Further, a traveling direction in which the wheelchair  1  moves backward is simply referred to as rearward, and the back of the wheelchair  1  corresponds to the back of the wheelchair user seated on the wheelchair  1 . The front-rear direction of the wheelchair  1  is also the longitudinal direction of the vehicle body. The left side of the wheelchair user sitting on the wheelchair  1  is the left side of the vehicle body of the wheelchair  1  and is simply referred to as the left. Further, the right side of the wheelchair user sitting on the wheelchair  1  is the right side of the vehicle body of the wheelchair  1  and is simply referred to as the right. The left-right direction of the wheelchair  1  is also the width direction of the vehicle body. Further, the “upper side” of the wheelchair  1  is a side which becomes the side of the top of the wheelchair  1  when the wheelchair  1  is placed on a horizontal surface in a state that can be seated. The “lower side” of the wheelchair  1  is a side which becomes the side of the bottom of the wheelchair  1  when the wheelchair  1  is placed on a horizontal surface in a state that can be seated. 
     (Configuration of Wheelchair Body) 
     As illustrated in  FIG. 1 ,  FIG. 4 , and the like, the wheelchair body  2  includes left- and right-side driving wheels  10 ,  11 , left side and right side casters  12 ,  13 , and left side and right side frames  20 ,  30 . The driving wheels  10 ,  11  are large-diameter wheels for the wheelchair user to rotate forward or backward while holding them by hand, and can also be called rear drive wheels because they are provided on the rear side of the wheelchair body  2 . The structure of the driving wheels  10 ,  11  is not particularly limited; however, in this embodiment, the driving wheels  10 ,  11  are configured by attaching rubber made tires  10   a ,  11   b  to wheels  10   a ,  11   a  made of carbon fiber-reinforced plastic (CFRP). On the outer side of the wheels  10   a ,  11   a  in the vehicle width direction, hand rims  10   c ,  11   c  to be held by the hand of the wheelchair user during driving are provided. Note that the reference character B in  FIG. 1 ,  FIG. 2 , and  FIG. 4  denotes a brake. The brake B is one that is traditionally well known, and is configured to be manually switched between a braking state and a release state. 
     The casters  12 ,  13  are wheels for changing the traveling direction of the wheelchair  1 , and are smaller in diameter than the driving wheels  10 ,  11 . Since the casters  12 ,  13  are arranged on the front side of the wheelchair body  2 , the casters  12 ,  13  can also be referred to as front wheels for changing traveling direction. 
     As illustrated in  FIG. 7 , the left-side frame  20  includes an upper frame part  21  extending in the front-rear direction and a caster support part  22 .  FIG. 7  illustrates the left-side frame  20  while the wheelchair  1  is placed on a horizontal surface. As illustrated in the figure, the upper frame part  21  is gently inclined upward toward the front. The inclination angle of the upper frame part  21  is not limited to that as illustrated, and may be horizontal. The upper frame part  21  and the caster support part  22  are formed as a single piece by the above-mentioned CFRP, and therefore the left-side frame  20  is formed by a single member. Note that the left-side frame  20  may be formed of a metal material, or by coupling a plurality of members. 
     In a rear end part of the upper frame part  21 , a wheel shaft insertion hole  21   a  is formed. To this wheel shaft insertion hole  21   a , the right side of a wheel shaft  10   d  of the left-side driving wheel  10  is inserted and fixed. The left-side driving wheel  10  is rotatably and pivotably supported about an axis extending in the left-right direction with respect to the left-side frame  20 , while the right side of the wheel shaft  10   d  being fixed to the rear end part of the upper frame part  21 . 
     In the front end part of the upper frame part  21 , a front-side protrusion  21   b  protruding forward is provided. The front-side protrusion  21   b  is configured to be foldable by the wheelchair user in the sitting state. In an intermediate part of the upper frame part  21  relative to the front-rear direction, a through-hole  21   c  penetrating the upper frame part  21  in the left-right direction is formed. With this hole, the weight of left-side frame  20  is reduced. The through-hole  21   c  may have a shape elongated in the front-rear direction. 
     In the rear end part of the upper frame part  21 , there is provided a rear-side recess  21   d  formed so as to be recessed forward. The rear-side recess  21   d  is a part to engage with a part of the seat  3 , as will be described later. 
     On the right-side surface of the upper frame part  21 , there is provided an accommodation recess  23  for accommodating a left-side seat frame member  90  of the seat  3  (described later). The accommodation recess  23  is open upward so that the seat frame member  90  can be accommodated in the accommodation recess  23  from above. The accommodation recess  23  also opens rightward, that is, inward relative to the width direction of the vehicle body, so that the inner surface of the accommodation recess  23  can be seen from the right side. 
     The accommodation recess  23  includes three parts. That is, the front-side part of the accommodation recess  23  is a front-side accommodation recess (left-side engagement recess)  24 , and the rear-side part of the accommodation recess  23  is a rear-side accommodation recess (left-side engagement recess)  25 . Further, a part between the front-side accommodation recess  24  and the rear-side accommodation recess  25  of the accommodation recess  23  is an intermediate accommodation recess  26 . Between the front-side accommodation recess  24  and the rear-side accommodation recess  25 , the through-hole  21   c  is positioned. Further, the through-hole  21   c  is positioned below the intermediate accommodation recess  26 . 
     The dimensions of the front-side accommodation recess  24  and the rear-side accommodation recess  25  in the depth direction (upward-downward direction) are set to be longer than the dimension of the intermediate accommodation recess  26  in the same direction. Thus, the front-side accommodation recess  24  and the rear-side accommodation recess  25  are formed with more depth than the intermediate accommodation recess  26 . The front-side accommodation recess  24  and the rear-side accommodation recess  25  have substantially the same dimension in the front-rear direction. The dimension of the intermediate accommodation recess  26  in the front-rear direction is set to be longer than those of the front-side accommodation recess  24  and the rear-side accommodation recess  25 . Thus, the intermediate accommodation recess  26  is longer in the front-rear direction. 
     The front and rear surfaces of the inner surface of the front-side accommodation recess  24  are a front-side engagement surface  24   a  and a rear-side engagement surface  24   b , respectively. The dimension of the front-side engagement surface  24   a  in the upward-downward direction is set to be longer than the dimension thereof in the left-right direction. Similarly, the dimension of the rear-side engagement surface  24   b  in the upward-downward direction is also set to be longer than the dimension thereof in the left-right direction. The front-side engagement surface  24   a  and the rear-side engagement surface  24   b  are formed so as to extend in the upward-downward direction, and get closer to each other toward the lower side. That is, the front-side engagement surface  24   a  is an inclined face inclined so as to be positioned rearward as it goes lower side, and the rear-side engagement surface  24   b  is an inclined face inclined so as to be positioned rearward as it goes lower side. Therefore, the distance between the front-side engagement surface  24   a  and the rear-side engagement surface  24   b  becomes narrower toward the lower side. The lower end parts of the front-side engagement surface  24   a  and the rear-side engagement surface  24   b  are apart from each other in the front-rear direction. 
     As illustrated in  FIG. 8 , the front-side engagement surface  24   a  and the rear-side engagement surface  24   b  are formed so as to get closer to each other toward the right side, that is, toward the inner side in the width direction of the vehicle body. That is, the front-side engagement surface  24   a  extends so as to be positioned rearward as it goes to the right side, and the rear-side engagement surface  24   b  extends so as to be positioned forward as it goes to the right side. The right edge part of the front-side engagement surface  24   a  and the rear-side engagement surface  24   b  are distanced from each other in the front-rear direction, and these parts are the parts at which the front-side accommodation recess  24  opens rightward. 
     A bottom surface  24   c  of the front-side accommodation recess  24  extends from the lower end part of the front-side engagement surface  24   a  to the lower end part of the rear-side engagement surface  24   b . Further, as illustrated in  FIG. 7 , a left-side surface  24   d  of the inner surface of the front-side accommodation recess  24  extends from the left end part of the front-side engagement surface  24   a  to the left end part of the rear-side engagement surface  24   b . In the left-side surface  24   d , a recessed part  24   e  to be a later-described engaged part is formed so as to be recessed leftward. The recessed part  24   e  is positioned substantially in the middle relative to the front-rear direction, in a position higher than the middle relative to the upward-downward direction, of the left-side surface  24   d . The shape of the recessed part  24   e  is not particularly limited; however, in this embodiment, the dimension in the front-rear direction is set to be longer than the dimension in the upward-downward direction, in a right side view. The depth (dimension in the left-right direction) of the recessed part  24   e  is set so that the middle part relative to the upward-downward direction is deepest. 
     The rear-side accommodation recess  25  is configured in the similar manner as the front-side accommodation recess  24 . Similarly to the front-side engagement surface  24   a  and the rear-side engagement surface  24   b  of the front-side accommodation recess  24 , the front-side engagement surface  25   a  and the rear-side engagement surface  25   b  of the rear-side accommodation recess  25  are formed so as to extend in the upward-downward direction, and get closer to each other toward the lower side. Further, as illustrated in  FIG. 8 , the front-side engagement surface  25   a  and the rear-side engagement surface  25   b  are formed so as to get closer to each other toward the right side. Further, as illustrated in  FIG. 7 , a bottom surface  25   c  of the rear-side accommodation recess  25  is positioned immediately above the wheel shaft insertion hole  21   a . In the left-side surface  25   d  of the inner surface of the rear-side accommodation recess  25 , a recessed part  25   e  to be an engaged part is formed so as to be recessed leftward. The shape of the recessed part  24   e  on the front side and the shape of the recessed part  25   e  on the rear side may be the same or different. 
     As illustrated in  FIG. 7 , the caster support part  22  extends obliquely downward toward the front from an intermediate part of the upper frame part  21  in the front-rear direction. As illustrated in  FIG. 8 , the caster support part  22  is curved so that its lower side is positioned on the left side, that is, on the outer side in the width direction of the vehicle body. As illustrated in  FIG. 4 , the lower end part of the caster support part  22  is in front of the left-side driving wheel  10 , apart from the left-side driving wheel  10  by a predetermined distance. To this lower end part, a left-side caster  12  is attached in such a manner as to be capable of pivot about a center axis extended in the upward-downward direction. The caster  12  is positioned directly below the front-side protrusion  21   b  of the upper frame part  21 . 
     As illustrated in  FIG. 2  and the like, the right-side frame  30  has a symmetrical configuration with respect to the left-side frame  20 , and includes an upper frame part  31  and a caster support part  32 . As illustrated in  FIG. 9 , in the upper frame part  31 , a wheel shaft insertion hole  31   a  is formed. To this wheel shaft insertion hole  31   a , the left side of a wheel shaft  11   d  (illustrated in  FIG. 14 ) of the right-side driving wheel  11  is inserted and fixed. The right-side driving wheel  11  is rotatably and pivotably supported about an axis extending in the left-right direction with respect to the right-side frame  30 , while the left side of the wheel shaft  11   d  being fixed to the rear end part of the upper frame part  31 . 
     As illustrated in  FIG. 10 , in the front end part of the upper frame part  31 , a front-side protrusion  31   b  is provided. Further, in an intermediate part of the upper frame part  31  relative to the front-rear direction, a through-hole  31   c  penetrating the upper frame part  31  in the left-right direction is formed. In the rear end part of the upper frame part  31 , there is provided a rear-side recess  31   d  (illustrated in  FIG. 9 ) formed so as to be recessed forward. Note that  FIG. 9  also illustrates a part of a right-side angle changer  84  that is a member constituting a part of the seat  3 . This right-side angle changer  84  is hiding a part of the rear end part of the upper frame part  31  in the figure. 
     As illustrated in  FIG. 2 , on the left-side surface of the upper frame part  31 , there is provided an accommodation recess  33  for accommodating a right-side seat frame member  91  of the seat  3  (described later). The accommodation recess  33  is open toward the upper side and left side, so that the inner surface of the accommodation recess  33  can be seen from the left side. 
     As illustrated in  FIG. 9  and  FIG. 10 , the accommodation recess  33  has a front-side accommodation recess (right-side engagement recess)  34 , a rear-side accommodation recess (right-side engagement recess)  35 , and an intermediate accommodation recess  36 . As illustrated in  FIG. 10 , a front-side engagement surface  34   a  and a rear-side engagement surface  34   b  of the front-side accommodation recess  34  are formed so as to extend in the upward-downward direction, and get closer to each other toward the lower side and toward the left side. The inner surface of the front-side accommodation recess  34  includes a bottom surface  34   c  and a right-side surface  34   d . In the right-side surface  34   d , a recessed part  34   e  to be an engaged part is formed so as to be recessed rightward. 
     As illustrated in  FIG. 9 , the rear-side accommodation recess  35  is configured in a similar manner as the front-side accommodation recess  34 , and the front-side engagement surface  35   a  and a rear-side engagement surface  35   b  are formed so as to extend in the upward-downward direction, and get closer to each other toward the lower side and toward the right side. Further, a bottom surface  35   c  of the rear-side accommodation recess  35  is positioned immediately above the wheel shaft insertion hole  31   a . Further, in the right-side surface  35   d  of the rear-side accommodation recess  35 , a recessed part  35   e  to be an engaged part is formed so as to be recessed rightward. 
     As illustrated in  FIG. 1  and the like, the caster support part  32  extends obliquely downward toward the front from an intermediate part of the upper frame part  31  in the front-rear direction, and is curved so that its lower side is positioned on the right side. To the lower end part of the caster support part  32 , a right-side caster  13  is attached in such a manner as to be capable of pivot about a center axis extended in the upward-downward direction. 
     (Configuration of Foot Rest Part) 
     As illustrated in  FIG. 1 , a foot rest part  40  on which the wheelchair user places his/her feet is provided in a front part of the wheelchair body  2 . The foot rest part  40  includes: a left-side rest arm  41  coupled to a lower end part of the caster support part  22  of the left-side frame  20  so as to be pivotable in the upward-downward direction; a right-side rest arm  42  coupled to a lower end part of the caster support part  32  of the right-side frame  30  so as to be pivotable in the upward-downward direction; and a coupling plate  43  that pivotably couples the right end part of the left-side rest arm  41  and the left end part of the right-side rest arm  42  with each other. The pivotal center lines extend in the front-rear direction. The left-side rest arm  41  has a left plate  41   a  for placing thereon the left foot, and the right-side rest arm  42  has a right plate  42   a  for placing thereon the right foot. 
     As illustrated in  FIG. 1  and  FIG. 2 , the left-side rest arm  41  and the right-side rest arm  42  extend horizontally while the wheelchair body  2  is in an unfolded state. While the wheelchair body  2  is in the folded state, on the other hand, the left-side rest arm  41  and the right-side rest arm  42  are folded in the left-right direction so as to take a posture of extending substantially in the upward-downward direction, with the coupling plate  43  arranged on top, as illustrated in  FIG. 5 . In short, the left-side rest arm  41  and the right-side rest arm  42  are pivotable relative to each other so as not to inhibit the folding operation of the wheelchair body  2 . 
     (Unfolding and Folding of Wheelchair Body) 
     The wheelchair body  2  can be changed from the unfolded state illustrated in  FIG. 1  and  FIG. 2  to the folded state illustrated in  FIG. 5  and  FIG. 6  and from the folded state to the unfolded state, without using a tool or the like. In the unfolded state, the distance between the left-side frame  20  and the right-side frame  30  expands and attachment of the seat  3  becomes possible. In the folded state, on the other hand, the distance between the left-side frame  20  and the right-side frame  30  is narrowed and attachment of the seat  3  is not possible. In the present embodiment, the seat  3  and the wheelchair body  2  are configured to be separable and attachable. By detaching the seat  3  from the wheelchair body  2  while the wheelchair  1  is not in use, the wheelchair body  2  and the seat  3  are separated from each other, which reduces the weight for carrying them and makes them compact. Further, since the wheelchair body  2  is foldable, the wheelchair body  2  is made compact. In the following, the configuration that makes the wheelchair body  2  foldable will be described in detail. 
     (Support Arm) 
     As an exemplary configuration that makes the wheelchair body  2  foldable, the present embodiment adopts a configuration using a plurality of support arms  51 ,  52 ,  61 ,  62 . Specifically, the wheelchair body  2  includes: a first left-side support arm  51  and a second left-side support arm  52  that are pivotably coupled to the left-side frame  20 , and a first right-side support arm  61  and a second right-side support arm  62  that are pivotably coupled to the right-side frame  30 . The first left-side support arm  51  and the first right-side support arm  61  have the same length and are laterally symmetrical. The second left-side support arm  52  and the second right-side support arm  62  have the same length and are laterally symmetrical. Further, the wheelchair body  2  also has a manually operable folding mechanism  70 . Note that the first left-side support arm  51  and the first right-side support arm  61  may be laterally asymmetrical, and that the second left-side support arm  52  and the second right-side support arm  62  may also be laterally asymmetrical. 
     As illustrated in  FIG. 11 , a base end part (one end part) of the first left-side support arm  51  is coupled to the left-side frame  20 , at a lower part on the front side of the middle part of the upper frame part  21  relative to the front-rear direction, via a coupling shaft  51   a  extending in the upward-downward direction in such a manner as to be pivotable in the front-rear direction. Further, a base end part (one end part) of the second left-side support arm  52  is coupled to the left-side frame  20 , at a lower part on the rear side of the middle part of the upper frame part  21  relative to the front-rear direction, via a coupling shaft  52   a  extending in the upward-downward direction in such a manner as to be pivotable in the front-rear direction. Thus, the second left-side support arm  52  is provided to the rear of the first left-side support arm  51 . 
     The right-side support arms  61 ,  62  are arranged in a similar manner as the left-side support arms  51 ,  52 , and a base end part (one end part) of the first right-side support arm  61  is coupled to the right-side frame  30 , at a lower part on the front side of the middle part of the upper frame part  31  relative to the front-rear direction, via a coupling shaft  61   a  extending in the upward-downward direction in such a manner as to be pivotable in the front-rear direction. Further, a base end part (one end part) of the second right-side support arm  62  is coupled to the right-side frame  30 , at a lower part on the rear side of the middle part of the upper frame part  31  relative to the front-rear direction, via a coupling shaft  62   a  extending in the upward-downward direction in such a manner as to be pivotable in the front-rear direction. The center lines of the four coupling shafts Ma,  52   a ,  61   a  and  62   a  are parallel to one another. Further, the four coupling shafts  51   a ,  52   a ,  61   a , and  62   a  may be vertical or inclined with respect to the vertical line, provided that they extend in the upward-downward direction. The folding operation is possible even if, for example, the four coupling shafts  51   a ,  52   a ,  61   a  and  62   a  are slightly inclined forward or backward. 
     For example, as illustrated in  FIG. 4 , when viewing the wheelchair  1  from the left while placing it on a horizontal plane, the upper frame part  21  of the left-side frame  20  is inclined so as to be positioned higher toward the front side. The upper frame part  31  of the right-side frame  30  is also inclined in the same manner. 
     Therefore, the first left-side support arm  51  and the first right-side support arm  61  positioned to the front of the second left-side support arm  52  and the second right-side support arm  62  are in positions higher than the second left-side support arm  52  and the second right-side support arm  62 . 
     As illustrated in  FIG. 1 ,  FIG. 2 , and  FIG. 11 , while the wheelchair body  2  is in the unfolded state, the left-side support arms  51 ,  52  and the right-side support arms  61 ,  62  all take a posture that extends in the left-right direction to spread the distance between the left-side frame  20  and the right-side frame  30 . During this state, the first left-side support arm  51  and the first right-side support arm  61  are aligned to form a straight line extending in the left-right direction, and the second left-side support arm  52  and the second right-side support arm  62  are aligned to form a straight line extending in the left-right direction. Further, a distal end part that is the right end part of the first left-side support arm  51  reaches to the middle between the left-side frame  20  and the right-side frame  30  in the left-right direction, and a distal end part that is the left end part of the first right-side support arm  61  also reaches to the middle between the left-side frame  20  and the right-side frame  30 . 
     On the other hand, as illustrated in  FIG. 5  and  FIG. 6 , the distance between the left-side frame  20  and the right-side frame  30  can be narrowed, thus folding the wheelchair body  2 , by: pivoting the first left-side support arm  51  about the coupling shaft  51   a  so that the distal end part (other end part) moves to the rear; pivoting the first right-side support arm  61  about the coupling shaft  61   a  so that the distal end part (other end part) moves to the rear; pivoting the second left-side support arm  52  about the coupling shaft  52   a  so that the distal end part (other end part) moves to the rear; and pivoting the second right-side support arm  62  about the coupling shaft  62   a  so that the distal end part (other end part) moves to the rear. During the folded state, the first left-side support arm  51  and the first right-side support arm  61  take a posture that extends in the front-rear direction, and the second left-side support arm  52  and the second right-side support arm  62  take a posture that extends in the front-rear direction. While the present embodiment deals with a case where the first left-side support arm  51  and the first right-side support arm  61  aligned in the left-right direction, and are parallel to each other, the present invention is not limited to this, and the first left-side support arm  51  and the first right-side support arm  61  does not have to be parallel to each other, and may be arranged so that the distance between the support arms  51 ,  61  is widened as it goes toward the based end. The similar applies to the second left-side support arm  52  and the second right-side support arm  62 . Note that, at the time of folding, the left-side rest arm  41  and the right-side rest arm  42  of the foot rest part  40  are pivoted upward, and a folding operation of the foot rest part  40  is performed at the same time. 
     Note that the left-side support arms  51 ,  52  and the right-side support arms  61 ,  62  are configured so as not to pivot forward from their positions in the unfolded state. That is, as illustrated in  FIG. 11 , when an attempt is made to pivot forward the first left-side support arm  51  from its position in the unfolded state, an edge part  51   b  on the base end side of the first left-side support arm  51  contacts the upper frame part  21 , thus inhibiting pivoting of the first left-side support arm  51  forward. The second left-side support arm  52  is also inhibited from pivoting forward by an edge part  52   b . Further, the first right-side support arm  61  is also inhibited from pivoting forward by an edge part  61   b . Further, the second right-side support arm  62  is also inhibited from pivoting forward by an edge part  62   b . The configuration for inhibiting the forward pivoting is not limited to the one described above, and another configuration, such as a configuration including a stopper or the like, is also possible. 
     (Folding Mechanism) 
     Next, the following describes the configuration of the folding mechanism  70  illustrated in  FIG. 11 ,  FIG. 12 , and the like. The folding mechanism  70  is arranged between the left-side frame  20  and the right-side frame  30 , and couples the first left-side support arm  51  and the first right-side support arm  61  in such a manner that the first left-side support arm  51  and the first right-side support arm  61  are foldable in the left-right direction, while coupling the second left-side support arm  52  and the second right-side support arm  62  in such a manner that the second left-side support arm  52  and the second right-side support arm  62  are foldable in the left-right direction. Specifically, the folding mechanism  70  includes a front-side coupling member  71 , a rear-side coupling member  72 , an interlocking member  73 , an operation part  74 , a grip part  75 , and a left-side driven gear part (first gear part)  76 , a right-side driven gear part (first gear part)  77 , and a driving gear part (second gear part)  78 . Only one of the left-side driven gear part  76  or the right-side driven gear part  77  may be provided. In the following, each member constituting the folding mechanism  70  will be described in detail. 
     (Driven Gear Part) 
     As illustrated in  FIG. 13 , the left-side driven gear part  76  is arranged integrally with the distal end part of the first left-side support arm  51 , so that the first left-side support arm  51  and the left-side driven gear part  76  do not pivot relatively to each other. In the distal end part of the first left-side support arm  51 , a support shaft  51   c  extending in the upward-downward direction is provided so as to penetrate the distal end part. The support shaft  51   c  is kept from coming off from the distal end part of the first left-side support arm  51 . A plurality of teeth constituting the left-side driven gear part  76  are aligned so as to draw an arc-shaped path about the support shaft  51   c  at the distal end part of the first left-side support arm  51 . Therefore, the rotational center line of the left-side driven gear part  76  extends in the upward-downward direction. 
     Similarly, as illustrated in  FIG. 11 , a plurality of teeth constituting the right-side driven gear part  77  are aligned so as to draw an arc-shaped path about a support shaft  61   c  that is kept from coming off from the distal end part of the first right-side support arm  61 . Therefore, the rotational center line of the right-side driven gear part  77  also extends in the upward-downward direction. The rotational center lines of the left-side driven gear part  76  and the right-side driven gear part  77  are parallel to the coupling shaft  51   a.    
     The left-side driven gear part  76  and the right-side driven gear part  77  are arranged in the left-right direction with a predetermined distance therebetween. The number of teeth of the left-side driven gear part  76  is the same as the number of teeth of the right-side driven gear part  77 . 
     (Coupling Members) 
     As illustrated in  FIG. 12 , the front-side coupling member  71  is made of a plate extended in the left-right direction, and two identical front-side coupling members  71  are provided, one at the tope and one at the bottom, with a distance there between. The distance between the front-side coupling members  71 ,  71  is set so as to accommodate the distal end sides of the first left-side support arm  51  and the first right-side support arm  61  between the front-side coupling members  71 ,  71 . A front part of the front-side coupling members  71  is coupled to the grip part  75 . Meanwhile, as illustrated in  FIG. 11 , the distal end part of the first left-side support arm  51  is coupled to a left-rear part of the front-side coupling member  71  by the support shaft  51   c . Further, the distal end part of the first right-side support arm  61  is coupled to a right rear part of the front-side coupling member  71  by the support shaft  61   c . The first left-side support arm  51  is pivotable about the support shaft  51   c , and the first right-side support arm  61  is pivotable about the support shaft  61   c . Thus, the distal end part of the first left-side support arm  51  and the distal end part of the first right-side support arm  61  are pivotably coupled to each other via the front-side coupling member  71 , and the rear end part (base end part) of the grip part  75  is coupled to the distal end part of the first left-side support arm  51  and the distal end part of the first right-side support arm  61  via the front-side coupling member  71 . The support shaft  61   c  is parallel to the coupling shaft  61   a.    
     The rear-side coupling member  72  is arranged to the rear of the front-side coupling member  71 , distanced from the same. The rear-side coupling member  72  has a thick plate shape extended in the front-rear direction and is coupled to the distal end part of the second left-side support arm  52  by a support shaft  72   a  extending in the upward-downward direction and to the distal end part of the second right-side support arm  62  by a support shaft  72   b . The second left-side support arm  52  is pivotable about the support shaft  72   a , and the second right-side support arm  62  is pivotable about the support shaft  72   b . The rear-side coupling member  72  has a cavity part  72   c  that accommodates therein the distal end side of the second left-side support arm  52  and the distal end side of the second right-side support arm  62 . The support shafts  72   a ,  72   b  are parallel to the coupling shaft  52   a . 
     In a rear part of the rear-side coupling member  72 , a ring part  72   d  formed in a ring shape is provided. The ring part  72   d  protrudes rearward from the second left-side support arm  52  and the second right-side support arm  62 . This ring part  72   d  may be provided as needed, and may be omitted or have a different shape. 
     (Interlocking Member) 
     The interlocking member  73  is a member that couples the front-side coupling member  71  and the rear-side coupling member  72 , and is formed in a rod shape extended in the front-rear direction. The rear end part of the interlocking member  73  is fixed to a front part of the rear-side coupling member  72 , in the middle relative to the left-right direction. On the other hand, the front end part of the interlocking member  73  is coupled pivotably with respect to the support shaft  51   c  at the distal end part of the first left-side support arm  51  and to the support shaft  61   c  at the distal end part of the first right-side support arm  61 . The distal end part of the first left-side support arm  51  and the distal end part of the first right-side support arm  61  are pivotable about the support shaft  51   c  and the support shaft  61   c , respectively, with respect to the front end part of the interlocking member  73 . Thus, the first left-side support arm  51  and the first right-side support arm  61  are coupled to and interlocked with the second left-side support arm  52  and the second right-side support arm  62  via the interlocking member  73 . 
     (Operation Part and Driving Gear Part) 
     The operation part  74  is a member to manually operate the folding mechanism  70  by, for example, the wheelchair user or a helper who performs folding operation (operator), and is arranged in the middle relative to the left-right direction between the left-side frame  20  and the right-side frame  30 . An operating direction of this operation part  74  is the upward-downward direction. That is, as illustrated in  FIG. 14  and  FIG. 15 , a support shaft (support member)  74   a  penetrates the base end part of the operation part  74  in the left-right direction. With this support shaft  74   a  the operation part  74  is pivotably supported. The left end part of the support shaft  74   a  is supported by a left-side bearing unit  74   b  and the right end part of the support shaft  74   a  is supported by a right-side bearing unit  74   c . The left-side bearing unit  74   b  is arranged on the left side of the upper surface of the front-side coupling member  71 , and is integrated with the upper end part of the support shaft  51   c . The right-side bearing unit  74   c  is arranged on the right side of the upper surface of the front-side coupling member  71 , and is integrated with the upper end part of the support shaft  61   c.    
     A part of the operation part  74  radially away from the support shaft  74   a  is formed in a ring shape. This enables the operator to insert his/her hand into the operation part  74  to grip the operation part  74  or hold the operation part  74 . The size of the operation part  74  can be set to any size, and is set to a size that at least allows insertion of a finger in one preferred embodiment. The operation part  74  does not have to be formed in a ring shape, and may be formed in a rod shape. In the case of forming the operation part  74  in a rod shape, the operation part  74  has a part radially extending from the support shaft  74  and a part extending parallel to the support shaft  74   a  in one preferred embodiment. 
     As illustrated in  FIG. 14 , the driving gear part  78  is integrally provided to the base end part of the operation part  74 , so that the driving gear part  78  and the base end part of the operation part  74  are kept from pivoting relatively to each other. A plurality of teeth constituting the driving gear part  78  are aligned so as to draw an arc-shaped path about the support shaft  74   a  at the base end part of the operation part  74 . Therefore, the rotational center line of the driving gear part  78  extends in the left-right direction. Since the operation part  74  and the driving gear part  78  are integrated with each other, the driving gear part  78  can be driven about the support shaft  74   a  by operating the operation part  74  to pivot about the support shaft  74   a . At this time, the operation part  74  pivots about the same rotational center line as that of the driving gear part  78 . That is, the support shaft  74   a  is a member that supports the operation part  74  so that the operation part  74  can be operated and pivoted about the same rotational center line as that of the driving gear part  78 . 
     The support shaft  74   a  is arranged above the first left-side support arm  51  and the first right-side support arm  61 . Therefore, the rotational center line of the driving gear part  78  and the operation part  74  are arranged above the first left-side support arm  51  and the first right-side support arm  61 . To operate the operation part  74 , the operation part  74  is held by a hand from the above. Since the operation part  74  is positioned above the first left-side support arm  51  and the first right-side support arm  61 , the first left-side support arm  51  and the first right-side support arm  61  do not obstacle the hand at the time of holding the operation part  74 , which improves the operability. 
     The width (dimension in the left-right direction) of the teeth of the driving gear part  78  is set so as to reach the left-side driven gear part  76  and the right-side driven gear part  77 . As a result, the teeth of the driving gear part  78  can be meshed with both the teeth of the left-side driven gear part  76  and the teeth of the right-side driven gear part  77 . That is, a single driving gear part  78  can drive two driven gear parts  76 ,  77 , which contributes to reduction of the number of parts. Further, it is possible to synchronize the pivot start timing and the pivoting speed between the driven gear parts  76 ,  77 . 
     The rotational center line of the driving gear part  78  extends in the left-right direction, while the rotational center lines of the left-side driven gear part  76  and the right-side driven gear part  77  extend in the upward-downward direction. Even in such a case where the rotational center lines are perpendicularly crossing, smooth transmission of power is possible by arranging the rotational center line of the driving gear part  78  above the left-side driven gear part  76  and the right-side driven gear part  77 . 
     (Folding and Unfolding Operations with Operation Part) 
     The folding mechanism  70  is configured to change the first left-side support arm  51  and the first right-side support arm  61 , and the second left-side support arm  52  and the second right-side support arm  62  from the folded state to the unfolded state or from the unfolded state to the folded state through operation of the operation part  74 . More specifically, the operation part  74  is capable of pivoting about the support shaft  74   a . By supporting the operation part  74  pivotably about the support shaft  74   a , the operation part  74  can be switched between an erected state (first operation state) in which the operation part  74  is erected upward as illustrated in  FIG. 5  and  FIG. 6 , and an unerected state (second operation state) in which the operation part  74  is reclined as illustrated in  FIG. 11 ,  FIG. 12 , and  FIG. 14 . In this embodiment, the operation part  74  in the erected state is switched to the unerected state by reclining the operation part  74  to the rear of the vehicle body. On the other hand, the operation part  74  in the unerected state is switched to the erected state by raising the operation part  74  toward the front of the vehicle body. The operation of reclining the operation part  74  toward the rear of the vehicle body is a downward operation, whereas the operation of raising the operation part  74  toward the front of the vehicle body is an upward operation. Note that, although illustration is omitted, the operation part  74  may be configured so as to be reclined toward the front of the vehicle body. 
     Through the operation of switching the unerected state of the operation part  74  to the erected state, the first left-side support arm  51  and the first right-side support arm  61  and the second left-side support arm  52  and the second right-side support arm  62  are changed from the unfolded state to the folded state. Further, through the operation of switching the erected state of the operation part  74  to the unerected state, the first left-side support arm  51  and the first right-side support arm  61  and the second left-side support arm  52  and the second right-side support arm  62  are changed from the folded state to the unfolded state. 
     More specifically, to switch the unerected state of the operation part  74  to the erected state, the operation part  74  is raised upward. This operation is an operation toward a predetermined direction. Since the operation part  74  is integrally provided with the driving gear part  78 , operation of the operation part  74  in the predetermined direction causes the driving gear part  78  to rotate forward about the support shaft  74   a . A rotational force of this rotation of the driving gear part  78  is transmitted to the left-side driven gear part  76  and the right-side driven gear part  77  meshed with the driving gear part  78 , causing the left-side driven gear part  76  and the right-side driven gear part  77  to try to rotate about their rotational center lines extended in the upward-downward direction. At this time, the base end part of the first left-side support arm  51  integrally having the left-side driven gear part  76  is pivotable about the coupling shaft  51   a  with respect to the left-side frame  20 . Further, the base end part of the first right-side support arm  61  integrally having the right-side driven gear part  77  is pivotable about the coupling shaft  61   a  with respect to the right-side frame  30 . Further, the distal end part of the first left-side support arm  51  and the distal end part of the first right-side support arm  61  are both pivotable with respect to the front-side coupling member  71 . Therefore, the rotational force transmitted to the left-side driven gear part  76  and the right-side driven gear part  77  causes the first left-side support arm  51  to pivot rearward about the coupling shaft  51   a  and causes the first right-side support arm  61  to pivot rearward about the coupling shaft  61   a . Thus, the first left-side support arm  51  and the first right-side support arm  61  in the unfolded state are changed to the folded state. 
     Since the first left-side support arm  51  and the first right-side support arm  61  are coupled to the second left-side support arm  52  and the second right-side support arm  62  via the interlocking member  73 , the second left-side support arm  52  and the second right-side support arm  62  also pivot similarly about the coupling shafts  52   a ,  62   a , respectively, in conjunction with pivoting of the first left-side support arm  51  and the first right-side support arm  61 . Thus, the second left-side support arm  52  and the second right-side support arm  62  in the unfolded state are changed to the folded state at the same time. 
     (Arrangement of Operation Part) 
     The following describes a case of lifting and carrying the wheelchair body  2  by one hand after folding the wheelchair body  2 . Wheelchairs in general are not expected to be lifted by one hand in the first place. Therefore, in a case of lifting the wheelchair body  2  by one hand, it is hard to find where to hold. Even if the wheelchair is held by one hand, the wheelchair that is not expected to be held by one hand is likely to become unstable and is likely to end up being inclined with its front part lower than its rear part. Since traditional wheelchairs in general have pivotable casters as in the present embodiment in its front part, the casters hang down and contacts the ground when the front part of the wheelchair is lowered. For this reason, the wheelchair needs to be lifted to a higher position. In particular, suppose that the wheelchair user drives a motor vehicle alone. In this case, the wheelchair user needs to move the wheelchair outside the motor vehicle to the inside after the wheelchair user has moved from the wheelchair to the driver seat of the motor vehicle. At this time, it is difficult to lift the wheelchair with both hands, and there is no choice but to lift the wheelchair by one hand. Doing so, however, causes the casters to hand down and contact the lower edge part of the door opening, causing difficulty to stow the wheelchair inside. It is therefore necessary to lift the wheelchair to a higher position, which is a significant burden for the wheelchair user. 
     To address this, the position of the operation part  74  is devised in this embodiment. Namely, as indicated by a broken line in  FIG. 4 , the operation part  74  is arranged between the wheel shafts  10   d ,  11   d  of the driving wheels  10 ,  11  and the rotational center lines of the casters  12 ,  13 , in a side view of the vehicle body. The center of gravity of the wheelchair body  2  with the seat  3  having been detached is in the vicinity of the wheel shafts  10   d ,  11   d  of the driving wheels  10 ,  11  in a side view. Therefore, holding the operation part  74  between the driving wheels  10 ,  11  and the casters  12 ,  13  in a side view after the wheelchair is folded causes the rear part of the wheelchair body  2  to be lower than the front part thereof. This inhibits the casters  12 ,  13  from hanging down. 
     (Grip Part) 
     As illustrated in  FIG. 11  and  FIG. 12 , the grip part  75  constituting a part of the folding mechanism  70  is a part that can be held at a time of moving the folded wheelchair body  2 . Although the operation part  74  may be held to lift the wheelchair body  2 , the operation part  74  is in the erected state while the wheelchair body  2  is folded, and some people may find it difficult to hold the operation part  74 . Further, it is imaginable that the operation part  74  in the ring shape could be hard to hold, and the operation part  74  is a member for operating the folding mechanism  70  in the first place and not a member exclusively for lifting the wheelchair body  2 . To address this, the present embodiment provides the grip part  75  separately from the operation part  74  to facilitate lifting of the wheelchair body  2 . Note that the grip part  75  may be omitted and the wheelchair body  2  may be lifted by holding the operation part  74 . 
     The grip part  75  is attached to the front part of the front-side coupling member  71 , and is coupled to the first left-side support arm  51  and the first right-side support arm  61  via the front-side coupling member  71 . The grip part  75  extends forward from the front part of the front-side coupling member  71 . That is, while the first left-side support arm  51  and the first right-side support arm  61  are in the folded state as illustrated in  FIG. 5  and  FIG. 6 , the distal end parts of the support arms  51 ,  61  are positioned rearward as compared to their base end parts. To change the first left-side support arm  51  and the first right-side support arm  61  in the folded state to the unfolded state, the first left-side support arm  51  and the first right-side support arm  61  are pivoted forward about the coupling shafts  51   a ,  61   a  by operating the operation part  74 . That is, the forward is the pivoting direction at the time of the changing the first left-side support arm  51  and the first right-side support arm  61  in the folded state to the unfolded state. 
     The grip part  75  can be used at the time of changing the wheelchair body  2  in the folded state to the unfolded state. When the wheelchair user holds the grip part  75  and makes a movement to lift the wheelchair body  2 , the grip part  75  coupled to both the first left-side support arm  51  and the first right-side support arm  61  moves relatively upward, because the first left-side support arm  51  and the first right-side support arm  61  are pivotably coupled to the left-side frame  20  and the right-side frame  30 , respectively, while a gravity-attributed downward force constantly acts on the left-side frame  20  and the right-side frame  30 . Due to this relative movement of the grip part  75 , the first left-side support arm  51  and the first right-side support arm  61  pivot forward until their folded state changes to the unfolded state. Since the grip part  75  extends forward which is the pivoting direction of both support arms  51 ,  61  at the time of changing from the folded state to the unfolded state, simply holding the grip part  75  and making a motion of lifting up unfold the wheelchair body  2  due to the weight of the wheelchair body  2  itself. To unfold by holding the grip part  75 , there is no need for operating the operation part  74 . 
     The shape and configuration of the grip part  75  are not particularly limited. In this embodiment, however, the grip part  75  is configured by a plurality of parts extending in different directions. Specifically, the grip part  75  includes a first grip part  75   a  linearly extended in the pivoting direction of the first left-side support arm  51  and the first right-side support arm  61  from a base end part (rear end part) coupled to the first left-side support arm  51  and the first right-side support arm  61 , and a second grip part  75   b  extended in the left-right direction of the vehicle body from the distal end part of the first grip part  75   a . The second grip part  75   b  may extend in both the left and right directions, or may extend only in one direction. Since the directions in which the first grip part  75   a  and the second grip part  75   b  extend are different from each other, the wheelchair user can select and hold the one he/she finds it easier to hold. 
     (Configuration of Seat) 
     As illustrated in  FIG. 2 , the seat  3  includes the seat cushion part  4  on which the wheelchair user is seated, the back cushion part  5 , and a seat frame  7 . As illustrated in  FIG. 1 , the seat frame  7  is detachably attachable to the left-side frame  20  and the right-side frame  30  of the wheelchair body  2 . As illustrated in  FIG. 3 , the seat frame  7  includes the left-side seat frame member  90 , a right-side seat frame member  91 , and a seat back frame  92 . As illustrated in  FIG. 1 , the left-side seat frame member  90  extends in the front-rear direction on the left side of the lower part of the seat  3 , along the upper frame part  21  of the left-side frame  20  of the wheelchair body  2 . The right-side seat frame member  91  extends in the front-rear direction on the right side of the lower part of the seat  3 , along the upper frame part  31  of the right-side frame  30  of the wheelchair body  2 . Note that the operation part  74  and the grip part  75  of the folding mechanism  70  are arranged between the left-side seat frame member  90  and the right-side seat frame member  91  in a plan view. 
     As illustrated by the virtual line in  FIG. 3 , the seat cushion part  4  constituting a seating surface for the wheelchair user to sit thereon extends from the left-side seat frame member  90  to the right-side seat frame member  91 , and also extends in the front-rear direction. The left side of the seat cushion part  4  is supported by the left-side seat frame member  90 , and the right side of the seat cushion part  4  is supported by the right-side seat frame member  91 . Examples of a member constituting the seat cushion part  4  include a plate material, a cloth material, a net-like member, various elastic materials, and a foam material. The seat cushion part  4  can be a member that can elastically deform downward when the wheelchair user sits thereon. 
     While the seat  3  is attached to the wheelchair body  2 , the seat cushion part  4  is arranged above the operation part  74  of the folding mechanism  70 . In other words, the operation part  74  is arranged directly below the seat cushion part  4 . For example, the seat cushion part  4  indicated by the virtual line in  FIG. 14  and the operation part  74  are apart from each other in the upward-downward direction, with a space formed therebetween. Such a relative positional relationship between the seat cushion part  4  and the operation part  74  can be established by the structure and shape of the seat frame  7 . 
     Specifically, the heights of the upper end parts of the seat frame members  90 ,  91  and the dimension of the seat frame members  90 ,  91  in the upward-downward direction are set so that the upper end part of the operation part  74  in the unerected state in a side view and the upper end parts of the seat frame members  90 ,  91  are distanced by at least a predetermined distance. This way, the operation part  74  in the unerected state in a side view is at least a predetermined distance below from the upper end part of the seat frame members  90 ,  91 , and as the result, the above-mentioned space is formed between the seat cushion part  4  and the operation part  74 . Here, when the wheelchair user sits on the seat cushion part  4 , the seat cushion part  4  sinks due to the weight of the wheelchair user. Since the operation part  74  is arranged at least a predetermined distance below the upper end parts of the seat frame members  90 ,  91  supporting the seat cushion part  4  in a side view, the operation part  74  does not contact the seat cushion part  4  having sunk. Thus, since the operation part  74  does not contact a part of the seat cushion part  4  corresponding to the legs or the buttocks of the wheelchair user, the wheelchair user does not feel awkwardness, and riding comfort is improved. 
     Note that the sinking amount of the seat cushion part  4  when the wheelchair user sits thereon increases with an increase in the weight of the wheelchair user. However, since the operation part  74  is arranged at least a predetermined distance below the upper end parts of the seat frame members  90 ,  91  as the reference, the seat cushion part  4  is kept from contacting the operation part  74  even if the seat cushion part  4  sinks due to a heavy wheelchair user sitting thereon. That is, the above-mentioned predetermined distance is set to such a value that the seat cushion part  4  is kept from contacting the operation part  74  even when the maximum load assumed for the wheelchair acts on the seat cushion part  4 . The maximum load assumed for the wheelchair can be set to any load. For example, the maximum load is a load in cases where a wheelchair user of  100  kg or  120  kg in his/her body weight is seated. The sinking amount of the seat cushion part  4  at this time can be referred to as a maximum sinking amount. Even when the sinking amount of the seat cushion part  4  is the maximum sinking amount, the lower surface of the seat cushion part  4  does not contact the operation part  74 . The above-mentioned predetermined distance may be changed according to the material, configuration, and the like of the seat cushion part  4 , because the sinking amount may be different depending on the material, configuration, and the like of the seat cushion part  4 . 
     The dimension of the operation part  74  and the height of the support shaft  74   a  are set so that the upper end part of the operation part  74  is in a position higher than the upper end parts of the seat frame members  90 ,  91 , while the operation part  74  is brought into the erected state as illustrated by the virtual line in  FIG. 14 . 
     Further, while the seat  3  is attached to the wheelchair body  2 , the grip part  75  is positioned below the seat cushion part  4 . Therefore, the grip part  75  is hidden under the seat cushion part  4 , which reduces the risk of the wheelchair user or the helper inadvertently gripping the grip part  75 . On the other hand, since the seat  3  is detached in an occasion of folding and holding the wheelchair body  2 , the grip part  75  can be seen from the above and the grip part  75  can be easily held. 
     (Fitting Configuration of Seat Frame and Wheelchair Body) 
     In this embodiment, at a time of attaching the seat  3  to the wheelchair body  2 , the seat frame  7  can be fit to the left-side frame  20  and the right-side frame  20  by placing both the left and right ends of the seat frame  7  on the left-side frame  20  and the right-side frame  20  of the wheelchair body  2 . Such a configuration of fitting suppresses rattling of the seat  3 . The following specifically describes the configuration of fitting the seat frame  7  to the wheelchair body  2 . 
     As illustrated in  FIG. 3 , on the front side of the left-side seat frame member  90 , there is provided a first left-side engagement protrusion  93  that protrudes downward. On the rear side of the left-side seat frame member  90 , there is provided a second left-side engagement protrusion  94 . The distance, in the front-rear direction, between the first left-side engagement protrusion  93  and the second left-side engagement protrusion  94  matches with the distance, in the front-rear direction, between the front-side accommodation recess  24  and the rear-side accommodation recess  25  (illustrated in  FIG. 7 ) formed on the left-side frame  20 . At a time of attaching the seat  3 , the first left-side engagement protrusion  93  and the second left-side engagement protrusion  94  are positioned above the front-side accommodation recess  24  and the rear-side accommodation recess  25  and then moved downward to insert the first left-side engagement protrusion  93  and the second left-side engagement protrusion  94 , from above, into the front-side accommodation recess  24  and the rear-side accommodation recess  25 . Therefore, the first left-side engagement protrusion  93  and the second left-side engagement protrusion  94  are parts that are inserted into the front-side accommodation recess  24  and the rear-side accommodation recess  25  from above and engages with them, respectively. Further, a part between the first left-side engagement protrusion  93  and the second left-side engagement protrusion  94  of the left-side seat frame member  90  is accommodated in the intermediate accommodation recess  26  formed in the left-side frame  20 . 
     The first left-side engagement protrusion  93  is formed in a hollowed shape, and the hollowed part is open to the left. A front surface  93   a  and a rear surface  93   b  on the front side and the rear side of the outer surface of the first left-side engagement protrusion  93  are formed so as to extend along the front-side engagement surface  24   a  and the rear-side engagement surface  24   b  of the front-side accommodation recess  24 . Therefore, the dimension of the first left-side engagement protrusion  93  in the front-rear direction is shortened toward the lower side. The lower surface of the first left-side engagement protrusion  93  is formed so as to extend along the bottom surface  24   c  of the front-side accommodation recess  24 . 
     The second left-side engagement protrusion  94  is also formed in a hollowed shape that is open to the left. A front surface  94   a  and a rear surface  94   b  on the front side and the rear side of the outer surface of the second left-side engagement protrusion  94  are formed so as to extend along the front-side engagement surface  25   a  and the rear-side engagement surface  25   b  of the rear-side accommodation recess  25 . Therefore, the dimension of the second left-side engagement protrusion  94  in the front-rear direction is shortened toward the lower side. The lower surface of the second left-side engagement protrusion  94  is formed so as to extend along the bottom surface  25   c  of the rear-side accommodation recess  25 . 
     The right-side seat frame member  91  is also provided with a first right-side engagement protrusion  95  and a second right-side engagement protrusion  96  that protrude downward, similarly to the left-side seat frame member  90 . The distance, in the front-rear direction, between the first right-side engagement protrusion  95  and the second right-side engagement protrusion  96  matches with the distance, in the front-rear direction, between the front-side accommodation recess  34  and the rear-side accommodation recess  35  formed on the right-side frame  30 . At a time of attaching the seat  3 , the first right-side engagement protrusion  95  and the second right-side engagement protrusion  96  are inserted from above into the front-side accommodation recess  34  and the rear-side accommodation recess  35 . Further, a part between the first right-side engagement protrusion  95  and the second right-side engagement protrusion  96  of the right-side seat frame member  91  is accommodated in the intermediate accommodation recess  36  formed in the right-side frame  30 . 
     The first right-side engagement protrusion  95  is formed in a hollowed shape that is open to the right. A front surface  95   a  and a rear surface  95   b  of the first right-side engagement protrusion  95  are formed so as to extend along the front-side engagement surface  34   a  and the rear-side engagement surface  34   b  of the front-side accommodation recess  34 . Therefore, the dimension of the first right-side engagement protrusion  95  in the front-rear direction is shortened toward the lower side. The lower surface of the first right-side engagement protrusion  95  is formed so as to extend along the bottom surface  34   c  of the front-side accommodation recess  34 . 
     The second right-side engagement protrusion  96  is also formed in a hollowed shape that is open to the right. A front surface  96   a  and a rear surface  96   b  of the second right-side engagement protrusion  96  are formed so as to extend along the front-side engagement surface  35   a  and the rear-side engagement surface  35   b  of the front-side accommodation recess  35 . Therefore, the dimension of the second right-side engagement protrusion  96  in the front-rear direction is shortened toward the lower side. The lower surface of the second right-side engagement protrusion  96  is formed so as to extend along the bottom surface  35   c  of the front-side accommodation recess  35 . 
     In the above-described configuration, the seat  3  can be attached to the wheelchair body  2  simply by moving the seat frame  7  downward so as to insert from above the left-side engagement protrusions  93 ,  94  and the right-side engagement protrusions  95 ,  96  into the left-side accommodation recesses  24 ,  25  and the right-side accommodation recesses  34 ,  35 , respectively. Therefore, the operation for attachment is easy. At the time of attaching operation, since the dimensions in the front-rear direction of the lower surfaces of the left-side engagement protrusions  93 ,  94  are shorter than the dimensions in the front-rear direction of the upper end parts of the left-side accommodation recesses  24 ,  25 , positioning of the left-side engagement protrusions  93 ,  94  and the left-side accommodation recesses  24 ,  25  is easily done. The similar applies to the right-side engagement protrusions  95 ,  96 . 
     By inserting the left-side engagement protrusions  93 ,  94  and the right-side engagement protrusions  95 ,  96  into the left-side accommodation recesses  24 ,  25  and the right-side accommodation recesses  34 ,  35  and engage them with each other, the seat frame  7  can be fit to the left-side frame  20  and the right-side frame  20 . At this time, since the front-side engagement surfaces  24   a ,  25   a  and the rear-side engagement surfaces  24   b ,  25   b  of the left-side accommodation recesses  24 ,  25 , the front-side engagement surfaces  34   a ,  35   a  and the rear-side engagement surface  34   b ,  35   b  of the right-side accommodation recesses  34 ,  35  are each formed so as to be closer to the corresponding counterpart as it goes to the lower side, the seat frame  7  can be easily positioned at the time of attachment operation, without seeing the engagement protrusions  93  to  96  and the accommodation recesses  24 ,  25 ,  34 ,  35 . Note that the seat frame  7  can also be easily detached as it only requires to lifting up the seat frame  7 . 
     Further, the weight of the wheelchair user pushes the left-side engagement protrusions  93 ,  94  and the right-side engagement protrusions  95 ,  96  of the seat frame  7  downward, when the wheelchair user sits on the seat cushion part  4 . As a result, the left-side engagement protrusions  93 ,  94  firmly contact the front-side engagement surfaces  24   a ,  25   a  and the rear-side engagement surfaces  24   b ,  25   b  of the left-side accommodation recesses  24 ,  25  and tightly fit into the left-side accommodation recesses  24 ,  25 . Further, the right-side engagement protrusions  95 ,  96  firmly contact the front-side engagement surfaces  34   a ,  35   a  and the rear-side engagement surface  34   b ,  35   b  of the right-side accommodation recesses  34 ,  35  and tightly fit into the right-side accommodation recesses  34 ,  35 . 
     The seat frame  7  includes a front-side cross beam  97  and a rear-side cross beam  98  extended in the left-right direction below the seat cushion part  4 . The front-side cross beam  97  extends from the right-side surface of the first left-side engagement protrusion  93  to the left-side surface of the first right-side engagement protrusion  95 , and is coupled to the first left-side engagement protrusion  93  and the first right-side engagement protrusion  95 . Further, the rear-side cross beam  98  extends from the right-side surface of the second left-side engagement protrusion  94  to the left-side surface of the second right-side engagement protrusion  96 , and is coupled to the second left-side engagement protrusion  94  and the second right-side engagement protrusion  96 . This embodiment deals with a case where the left-side seat frame member  90 , the right-side seat frame member  91 , the front-side cross beam  97 , and the rear-side cross beam  98  are integrally formed by the above-mentioned CFRP or the like; however, the present invention is not limited to this, and these parts may be separately formed and then combined into a single member. 
     With the front-side cross beam  97  and the rear-side cross beam  98 , not only is it possible to improve the rigidity of the seat frame  7  but also the rigidity of the wheelchair body  2  can be improved by indirect coupling of the left-side frame  20  and the right-side frame  30  of the wheelchair body  2  via the cross beams  97 ,  98  of the seat frame  7 . Especially, by combining and integrating the left-side engagement protrusions  93 ,  94  fit to the left-side frame  20  with the right-side engagement protrusions  95 ,  96  fit to the right-side frame  30 , the improved rigidity effect of the wheelchair body  2  becomes further remarkable. 
     (Seat Folding Configuration) 
     The seat  3  is configured to be foldable by folding down the part to serve as the backrest. That is, the seat back frame  92  is attached to the rear end parts of the left-side seat frame member  90  and the right-side seat frame member  91  so as to be pivotable about a rotational center line extended in the left-right direction, and is a member capable of supporting the back of the wheelchair user during the erected state. 
     Specifically, the seat back frame  92  includes a left-side rod member  80  and a right-side rod member  81  that are arranged so as to extend in the upward-downward direction during the erected state, and a coupling rod member  82  that couples intermediate parts of the left-side rod member  80  and the right-side rod member  81 . To the left-side rod member  80  and the right-side rod member  81 , the back cushion part  5  made of a material similar to the seat cushion part  4  is attached. While the seat back frame  92  is folded, the left-side rod member  80  and the right-side rod member  81  extend forward and are positioned above the seat cushion part  4 . Thus, the seat  3  can be made compact. 
     As the folding configuration of the seat back frame  92 , a traditionally known configuration can be adopted. In this embodiment, the left-side rod member  80  has a left-side angle changer  83 . The left-side angle changer  83  is arranged at the lower end part of the left-side rod member  80  and is coupled to the rear end part of the left-side seat frame member  90 . Further, the right-side rod member  81  has a right-side angle changer  84 . The right-side angle changer  84  is arranged at the lower end part of the right-side rod member  81  and is coupled to the rear end part of the right-side seat frame member  91 . 
     The right-side angle changer  84  includes a fixed member  84   a  fixed to the rear end part of the right-side seat frame member  91 , and a pivotable member  84   b  fixed to the lower end part of the right-side rod member  81  so as to be pivotable with respect to the fixed member  84   a , about the rotational center line extending in the left-right direction, and a lock pin  84   c . The lock pin  84   c  is inserted into a lock hole (not shown) formed in the fixed member  84   a  and into one of a first through hole or a second through hole (both not shown) formed in the pivotable member  84   b . The first through hole and the second through hole of the pivotable member  84   b  are arranged distanced from each other, in the circumferential direction of the pivotal center line of the seat back frame  92 . The positions of the first through hole and the second through hole are set so that, for example, the seat back frame  92  can be maintained in the erected state by inserting the lock pin  84   c  into the first through hole of the pivotable member  84   b  and the lock hole of the fixed member  84   a , while the seat back frame  92  can be maintained in the folded state by inserting the lock pin  84   c  into the second through hole of the pivotable member  84   b  and the lock hole of the fixed member  84   a.    
     The left-side angle changer  83  also includes a fixing member  83   a , a pivotable member  83   b , and a lock pin (not shown), similarly to the right-side angle changer  84 . Further, the lock pin  84   c  of the right-side angle changer  84  and the lock pin of the left-side angle changer  83  are coupled to each other via a lock pin coupler  85 . For example, pulling the lock pin coupler  85  can pull out the lock pin  84   c  of the right-side angle changer  84  and the lock pin of the left-side angle changer  83  from the lock holes, thus releasing the locked state. 
     The pivotable member  83   b  of the left-side angle changer  83  is provided with a left-side engagement part  83   d  that fits in and engages with the rear-side recess  21   d  of the left-side frame  20  while the seat back frame  92  is in the erected state. Similarly, the pivotable member  84   b  of the right-side angle changer  84  is provided with a right-side engagement part  84   d  that fits in and engages with the rear-side recess  31   d  of the right-side frame  30  while the seat back frame  92  is in the erected state. While the seat back frame  92  is folded, the left-side engagement part  83   d  and the right-side engagement part  84   d  moves upward and are out of the rear-side recess  21   d  of the left-side frame  20  and the rear-side recess  31   d  of the right-side frame  30 . 
     Further, the pivotable member  83   b  of the left-side angle changer  83  has a left-side pushing part  83   e  that pushes a later-described left-side slide member  113  to a lock position when the seat back frame  92  is turned to the erected state. The left-side pushing part  83   e  and the left-side engagement part  83   d  are integrated with each other. Further, the pivotable member  84   b  of the right-side angle changer  84  has a right-side pushing part  84   e  that pushes a later-described right-side slide member  103  (illustrated in  FIG. 17  and the like) to a lock position when the seat back frame  92  is turned to the erected state. The right-side pushing part  84   e  and the right-side engagement part  84   d  are integrated with each other. When the seat back frame  92  is folded, the left-side pushing part  83   e  and the right-side pushing part  84   e  are moved upward and separated upward from the left-side slide member  113  and the right-side slide member  103 , respectively. On the other hand, when the seat back frame  92  is turned to the erected state, the left-side pushing part  83   e  and the right-side pushing part  84   e  push forward the left-side slide member  113  and the right-side slide member  103  with a predetermined force or more, respectively. 
     (Lock Configuration of Seat to Wheelchair Body) 
     The seat  3  includes a lock configuration that keeps the seat  3  in a state of being attached to the wheelchair body  2  and restrict the seat  3  from easily detached from the wheelchair body  2 . As illustrated in  FIG. 17 , the right-side seat frame member  91  includes a first right-side lock member  101 , a second right-side lock member  102 , the single right-side slide member  103 , and a right-side coil spring (biasing member)  104 . The first right-side lock member  101  and the second right-side lock member  102  are identical to each other and are made of, for example, an elastic metal plate material, a resin material, or the like. 
     The first right-side lock member  101  is arranged on the front side of the right-side surface of the right-side seat frame member  91  and is positioned to overlap the recessed part  34   e  (illustrated in  FIG. 10 ) formed in the front-side accommodation recess  34  of the right-side frame  30 , in a side view. In a side view, the first right-side lock member  101  and the front-side cross beam  97  overlap each other. 
     Further, the second right-side lock member  102  is arranged on the rear side of the right-side surface of the right-side seat frame member  91  and is positioned to overlap the recessed part  35   e  (illustrated in  FIG. 9 ) formed in the rear-side accommodation recess  35  of the right-side frame  30 , in a side view. In a side view, the second right-side lock member  102  and the rear-side cross beam  98  overlap each other. 
     While the lower part of the first right-side lock member  101  is a fixed end fixed to the right-side surface of the right-side seat frame member  91 , the upper part is a free. Thus, the first right-side lock member  101  is flexibly deformable in the left-right direction. The middle part of the first right-side lock member  101  in the upward-downward direction is a part that enters the recessed part  34   e  and protrudes rightward as compared to the upper part and the lower part. Pushing the first right-side lock member  101  rightward with a predetermined force or more maintains a state in which the middle part of the first right-side lock member  101  protrudes from the right-side surface of the right-side seat frame member  91  toward the right side of the right-side seat frame member  91  and enters the recessed part  34   e . The first right-side lock member  101  is formed as described above. With the middle part of the first right-side lock member  101  in the recessed part  34   e , the middle part contacts and engages with the inner surface of the recessed part  34   e  to keep the middle part from coming off. Therefore, this state of the middle part protruding is the locked state. As described, since the recessed part  34   e  to serve as the engaged part is provided to a part of the right-side frame  30  corresponding to the first right-side lock member  101 , the locked state is achievable simply by forming the first right-side lock member  101  in the shape as hereinabove described. 
     On the other hand, a state in which the first right-side lock member  101  is movable toward the inside of the right-side seat frame member  91  is the unlocked state. In the unlocked state, the first right-side lock member  101  is elastically deformable toward the left. For example, when the seat frame  7  is lifted upward while the wheelchair body  2  is placed, the first right-side lock member  101  slides on the inner surface of the recessed part  34   e  and pushed leftward to be elastically deformed toward the left. This way, the first right-side lock member  101  comes out of the recessed part  34   e . Once the first right-side lock member  101  is out of the recessed part  34   e , the shape of the first right-side lock member  101  is restored. 
     Similarly to the first right-side lock member  101 , the lower part of the second right-side lock member  102  is a fixed end and the upper part of the same is a free end. The middle part of the second right-side lock member  102  enters and engaged with the recessed part  35   e . On the other hand, when the second right-side lock member  102  is in the unlocked state, the middle part of the second right-side lock member  102  can exit the recessed part  35   e.    
     As illustrated in  FIG. 17 , the right-side slide member  103  and the right-side coil spring  104  are accommodated in the right-side seat frame member  91 . The right-side slide member  103  is formed in a rod-like shape long in the front-rear direction and arranged to the left of the first right-side lock member  101  and the second right-side lock member  102  in the right-side seat frame member  91 , and is maintained slidable in the front-rear direction in the right-side seat frame member  91 . The right-side slide member  103  is movably guided only in the front-rear direction by the right-side seat frame member  91 . The right-side slide member  103  is slidable between a lock position that maintains the locked state of the first right-side lock member  101  and the second right-side lock member  102 , and the unlock position that brings the first right-side lock member  101  and the second right-side lock member  102  to the unlocked state. Thus, a single right-side slide member  103  switches the first right-side lock member  101  and the second right-side lock member  102  between the locked state and the unlocked state. 
     That is, the length of the right-side slide member  103  is set to be longer than the dimension of the right-side seat frame member  91  in the front-rear direction. In a part of the right-side slide member  103  closer to its rear, there is formed a spring contact part  103   a  to which the rear end part of the right-side coil spring  104  contacts. The front end part of the right-side coil spring  104  contacts the inner surface of the right-side seat frame member  91 , and the biasing force exerted by this right-side coil spring  104  acts on the right-side slide member  103  as a force that constantly biases the right-side slide member  103  rearward. In this embodiment, although the right-side slide member  103  is maintained in a state of having been slid rearward by the biasing force from the right-side coil spring  104 , the right-side slide member  103  slides forward against the biasing force from the right-side coil spring  104  with operation of attaching the seat  3  to the wheelchair body  2 , as hereinafter described. The position of the right-side slide member  103  having been slid rearward is the unlock position, whereas the position of the right-side slide member  103  having slid forward is the lock position. 
     To a part of the right-side slide member  103  closer to the front, a front-side regulator  103   b  is provided. When the right-side slide member  103  is slid to the rear and in the unlock position, the front-side regulator  103   b  is positioned to the rear of the first right-side lock member  101 . When the right-side slide member  103  is slid forward and in the lock position, the front-side regulator  103   b  is positioned to contact the left-side surface of the first right-side lock member  101 . The front-side regulator  103   b  is configured to push out the left-side surface of the first right-side lock member  101  to the right with a predetermined force or more so as to bring the first right-side lock member  101  into the locked state. That is the front-side regulator  103   b  is a member that causes the first right-side lock member  101  to be in the locked state and regulate retraction of the first right-side lock member  101  by contacting the first right-side lock member  101  in the locked state. 
     To a part of the right-side slide member  103  further rearward of the spring contact part  103   a , a rear-side regulator  103   c  is provided. When the right-side slide member  103  is slid to the rear and in the unlock position, the rear-side regulator  103   c  is positioned to the rear of the second right-side lock member  102 . When the right-side slide member  103  is slid forward and in the lock position, the rear-side regulator  103   c  is positioned to contact the left-side surface of the second right-side lock member  102 . The rear-side regulator  103   c  is configured in a similar manner as the front-side regulator  103   b  and is a member that causes the second right-side lock member  102  to be in the locked state and regulate retraction of the second right-side lock member  102  by contacting the second right-side lock member  102  in the locked state. 
     As is also illustrated in  FIG. 16 , the rear end part of the right-side slide member  103  having been slid to the unlock position protrudes rearward from the rear end surface of the right-side seat frame member  91 . On the other hand, the front end part of the right-side slide member  103  in the unlock position is within the right-side seat frame member  91 . When the right-side slide member  103  slides forward to the lock position as illustrated in  FIG. 19 , the front end part of the right-side slide member  103  protrudes forward from the front end surface of the right-side seat frame member  91 . 
     The front end part of the right-side slide member  103  engages with the right-side frame  30 . As illustrated in  FIG. 10 , a right-side insertion hole (insertion part)  34   f  to serve as an engaging hole is formed on the front side of the upper frame part  31  of the right-side frame  30 . The right-side insertion hole  34   f  is formed in a part of the upper frame part  31  corresponding to the front end part of the right-side slide member  103 , and opens at the front-side engagement surface  34   a  of the front-side accommodation recess  34 . Thus, the front end part of the right-side slide member  103  in the lock position is inserted into the right-side insertion hole  34   f  from the opening at the front-side engagement surface  34   a.    
     The right-side slide member  103  in the unlock position is switched to the lock position in conjunction with operation of attaching the seat  3  to the wheelchair body  2 . Specifically, the seat back frame  92  is folded down as illustrated in  FIG. 16  before the seat  3  is attached to the wheelchair body  2 . After that, the seat frame  7  is placed and fit to the left-side frame  20  and the right-side frame  30  of the wheelchair body  2  as illustrated in  FIG. 18 . Next, when the seat back frame  92  is pivoted to the erected state as illustrated in  FIG. 19 , the right-side pushing part  84   e  contacts the rear end part of the right-side slide member  103  and pushes the right-side slide member  103  forward with a predetermined force or more. This switches the right-side slide member  103  in the unlock position to the lock position in conjunction with the operation of bringing the seat back frame  92  to the erected state, and the first right-side lock member  101  and the second right-side lock member  102  are brought into the locked state and engages with the recessed parts  34   e ,  35   e . At the same time, the front end part of the right-side slide member  103  is inserted and engaged with the right-side insertion hole  34   f  from the opening at the front-side engagement surface  34   a . Therefore, the front end part of the right-side seat frame member  91  is restricted from being lifted up when the wheelchair user is seated. 
     Further, as illustrated in  FIG. 3 , the left-side seat frame member  90  includes a first left-side lock member  111 , a second left-side lock member  112 , the single left-side slide member  113 , and a left-side coil spring (biasing member)  114 , similarly to the right-side seat frame member  91 . 
     The first left-side lock member  111  is arranged on the front side of the left-side surface of the left-side seat frame member  90  and is positioned to overlap the recessed part  24   e  (illustrated in  FIG. 7 ) formed in the front-side accommodation recess  24  of the left-side frame  20 , in a side view. In a side view, the first left-side lock member  111  and the front-side cross beam  97  overlap each other. 
     Further, the second left-side lock member  112  illustrated in  FIG. 3  is arranged on the rear side of the left-side surface of the left-side seat frame member  90  and is positioned to overlap the recessed part  25   e  (illustrated in  FIG. 7 ) formed in the rear-side accommodation recess  25  of the left-side frame  20 , in a side view. In a side view, the second left-side lock member  112  and the rear-side cross beam  98  overlap each other. 
     The middle part of the first left-side lock member  111  relative to the upward-downward direction protrudes from the left-side surface of the left-side seat frame member  90  toward the left side of the left-side seat frame member  90  and enters the recessed part  24   e . With the middle part of the first left-side lock member  111  in the recessed part  24   e , the middle part contacts and engages with the inner surface of the recessed part  24   e . Further, the middle part of the second left-side lock member  112  relative to the upward-downward direction enters and engages with the recessed part  25   e.    
     The left-side slide member  113  and the left-side coil spring  114  are accommodated in the left-side seat frame member  90 . The right-side slide member  103  is arranged to the right of the first left-side lock member  111  and the second left-side lock member  112 , and is maintained slidable in the front-rear direction in the left-side seat frame member  90 . The left-side slide member  113  is slidable between a lock position that maintains the locked state of the first left-side lock member  111  and the second left-side lock member  112 , and the unlock position that brings the first left-side lock member  111  and the second left-side lock member  112  to the unlocked state. 
     In a part of the left-side slide member  113  closer to its rear, there is formed a spring contact part  113   a  to which the rear end part of the left-side coil spring  114  contacts. To a part of the left-side slide member  113  closer to the front, a front-side regulator  113   b  that contacts the first left-side lock member  111  is provided. To a part of the left-side slide member  113  further rearward of the spring contact part  113   a , a rear-side regulator  113   c  that contacts the second left-side lock member  112  is provided. 
     The rear end part of the left-side slide member  113  in the unlock position protrudes rearward from the rear end surface of the left-side seat frame member  90 . On the other hand, the front end part of the left-side slide member  113  in the unlock position is within the left-side seat frame member  90 . When the left-side slide member  113  slides forward to the lock position, the front end part of the left-side slide member  113  protrudes forward from the front end surface of the left-side seat frame member  90 . 
     The front end part of the left-side slide member  113  engages with the left-side frame  20 . Although illustration is omitted, a left-side insertion hole (insertion part) is formed on the front side of the upper frame part  21  of the left-side frame  20 . The left-side insertion hole is formed in a part of the upper frame part  21  corresponding to the front end part of the left-side slide member  113 , and opens at the front-side engagement surface  24   a  of the front-side accommodation recess  24 . Thus, the front end part of the left-side slide member  113  in the lock position is inserted into the left-side insertion hole from the opening at the front-side engagement surface  24   a . 
     The left-side slide member  113  in the unlock position is also switched to the lock position in conjunction with operation of attaching the seat  3  to the wheelchair body  2 . When the seat back frame  92  is brought into the erected state, the left-side pushing part  83   e  contacts the rear end part of the left-side slide member  113  and pushes the left-side slide member  113  forward with a predetermined force or more. This brings the first left-side lock member  111  and the second left-side lock member  112  into the locked state and engages them with the recessed parts  24   e ,  25   e . At the same time, the front end part of the left-side slide member  113  is inserted and engaged with the left-side insertion hole. Therefore, the front end part of the left-side seat frame member  90  is restricted from being lifted up when the wheelchair user is seated. 
     (Variation  1 ) 
       FIG. 20  to  FIG. 22  are related to Variation  1  of the embodiment. Variation  1  is different from the above-described embodiment in that an elevation member  120  is used when switching the right-side slide member  103  in the unlock position to the lock position. Namely, to the rear end part of the right-side slide member  103 , there is provided a sliding face  103   e  that is accommodated in the right-side seat frame member  91 , and the elevation member  120  that slides on the sliding face  103   e  is held in the right-side seat frame member  91  in a slidable manner. The sliding face  103   e  is inclined so as to be higher toward the rear. Further, the upper surface of the elevation member  120  is a surface that slides on the sliding face  103   e , and is inclined to be higher toward the rear side. On the lower side of the elevation member  120 , there is provided a pin part  120   a  that penetrates the right-side seat frame member  91  and protrudes downward. Further, the right-side seat frame member  91  accommodates therein a spring  121  that constantly biases the elevation member  120  downward. 
     When the seat  3  is detached from the wheelchair body  2  in Variation  1  as illustrated in  FIG. 20 , the biasing force from the spring  121  moves the elevation member  120  to a down-end position and the right-side slide member  103  retracts to the unlock position. When the seat  3  in this state is attached to the wheelchair body  2 , the pin part  120   a  of the elevation member  120  is pushed upward by the inner surface of the rear-side accommodation recess  35  of the upper frame part  31 , as illustrated in  FIG. 21 . Therefore, the elevation member  120  rises against the biasing force from the spring  121 . As the elevation member  120  rises, the upper surface of the elevation member  120  slides on the sliding face  103   e  of the right-side slide member  103 . Since the sliding face  103   e  is inclined so as to be higher toward the rear side, a forward force acts on the right-side slide member  103 , thereby switching the right-side slide member  103  to the lock position. In short, the right-side slide member  103  in the unlock position is switched to the lock position in conjunction with operation of attaching the seat frame  7  to the wheelchair body  2 . Further, by switching the right-side slide member  103  to the lock position, the first right-side lock member  101  and the second right-side lock member  102  are also turned to the locked state. Note that the similar configuration can be applied to the left side. 
     (Variation  2 ) 
       FIG. 23  to  FIG. 25  are related to Variation  2  of the embodiment. Variation  2  is different from the above-described embodiment in that a cam  130  is used when switching the right-side slide member  103  in the unlock position to the lock position. Namely, the rear end part of the right-side slide member  103  is accommodated in the right-side seat frame member  91 , and a cam  130  that contacts the rear end part is provided to the rear end part of the right-side seat frame member  91 . The cam  130  is provided to the right-side seat frame member  91  in such a manner as to be pivotable about an axis  130   a  extending in the left-right direction. A rear part  130   b  of the cam  130  protrudes rearward from the right-side seat frame member  91 . On the other hand, a front part  130   c  of the cam  130  extends to a position higher than the axis  130   a , and is arranged to contact the rear end part of the right-side slide member  103 . 
     When the seat  3  is detached from the wheelchair body  2  in Variation  2  as illustrated in  FIG. 23 , the biasing force from the right-side coil spring  104  moves and maintains the right-side slide member  103  in the unlock position and the rear end part of the right-side slide member  103  pushes the front part  130   c  of the cam  130  rearward and maintains the cam  130  in the position illustrated in the figure. When the seat  3  is attached to the wheelchair body  2  in this state, the rear part  130   b  of the cam  130  is pushed forward by the inner surface of the rear-side accommodation recess  35  of the upper frame part  31 , causing the cam  130  to try to pivot forward. The pivoting force of the cam  130  is transmitted from the front part  130   c  to the rear end part of the right-side slide member  103 , thus switching the right-side slide member  103  to the lock position as illustrated in  FIG. 24 . In short, the right-side slide member  103  in the unlock position is switched to the lock position in conjunction with operation of attaching the seat frame  7  to the wheelchair body  2 . Further, by switching the right-side slide member  103  to the lock position, the first right-side lock member  101  and the second right-side lock member  102  are also turned to the locked state. Note that the similar configuration can be applied to the left side. 
     (Variation  3 ) 
       FIG. 26  to  FIG. 28  are related to Variation  3  of the embodiment. Variation  3  is different from the above-described embodiment in that the inner surface of the rear-side accommodation recess  35  of the upper frame part  31  is used when switching the right-side slide member  103  in the unlock position to the lock position. Namely, when the seat  3  is attached to the wheelchair body  2  as illustrated in  FIG. 27 , the rear end part of the right-side slide member  103  contacts the rear-side engagement surface  35   b  of the rear-side accommodation recess  35  of the upper frame part  31 . This way, the right-side slide member  103  is pushed forward by the rear-side engagement surface  35   b  and switched to the lock position. In short, the right-side slide member  103  in the unlock position is switched to the lock position in conjunction with operation of attaching the seat frame  7  to the wheelchair body  2 . 
     Variation  3  includes an operation lever  150  for manually operating the right-side slide member  103 . The operation lever  150  can be provided on the rear side of the right-side slide member  103 . To the lower end part of the operation lever  150 , a shaft  150   a  extended in the left-right direction is provided. With this shaft  150   a , the operation lever  150  is freely pivotable with respect to the right-side slide member  103 . As described hereinabove, while the right-side slide member  103  is in the lock position, the first right-side lock member  101  and the second right-side lock member  102  are also in the locked state, and the seat frame  7  cannot be detached. In this variation, by pivoting the operation lever  150  rearward, the right-side slide member  103  in the lock position can be slid further forward. This causes the front-side regulator  103   b  and the rear-side regulator  103   c  to move to the forward of the first right-side lock member  101  and the second right-side lock member  102 , thus switching the first right-side lock member  101  and the second right-side lock member  102  to the unlocked state. By lifting the seat frame  7  obliquely rearward during this state, the right-side slide member  103  can be pulled out from the right-side insertion hole  34   f , making the seat frame  7  detachable. 
     Alternatively, instead of providing the operation lever  150  in Variation  3 , the rear end part of the right-side slide member  103  may be positioned higher than the intermediate part relative to the front-rear direction. This way, the rear end part of the right-side slide member  103  can be manually operated. 
     (Action and Advantages of Embodiment) 
     As described hereinabove, according to this embodiment, the wheelchair body  2  can be folded by operating the operation part  74  of the folding mechanism  70  in the upward-downward direction. Therefore, the folding operation can be done with one hand without a need for pulling a part of the wheelchair body  2 , the driving wheel, or the like, and convenience can be improved. 
     Further, since the operation part  74  of the folding mechanism  70  is arranged below the upper end part of the left-side seat frame member  90  and the right-side seat frame member  91  with a predetermined space therebetween, the operation part  74  does not cause a wheelchair user seated to feel awkward, and a comfortable riding is achieved. 
     Further, since the operation part  74  of the folding mechanism  70  is arranged between the driving wheels  10 ,  11  and the casters  12 ,  13  in a side view of the vehicle body, it is possible to avoid the casters  12 ,  13  from hanging when the wheelchair  1  is lifted by holding the operation part  74 . Thus, the wheelchair  1  lifted can be easily moved. 
     Further, there is provided a grip part  75  extended in a pivoting direction of the support arms  51 ,  61  at a time of switching from the folded state to the unfolded state. Therefore, at a time of unfolding the wheelchair body  2 , the wheelchair body  2  can be unfolded by one hand, using the weight of the wheelchair body  2  itself. 
     Further, each of the front-side engagement surfaces  24   a ,  25   a ,  34   a ,  35   a  and the rear-side engagement surfaces  24   b ,  25   b ,  34   b ,  35   b  of the accommodation recesses  24 ,  25 ,  34 ,  35  provided to the side frames  20 ,  30  of the wheelchair body  2  are formed so as to be closer to the corresponding counterpart as it goes to the lower side. Therefore, the seat frame  7  can be easily attached to or detached from the wheelchair body  2 , and is firmly fixed to the wheelchair body  2  at a time of attaching the seat frame  7 . 
     Further, since the lock members  101 ,  102 ,  111 ,  112  of the seat frame  7  can be engaged in conjunction with the recessed parts  24   e ,  25   e ,  34   e ,  35   e  of the wheelchair body  2  in conjunction with operation of attaching the seat frame  7  to the wheelchair body  2 , the seat frame  7  can be tightly attached to the wheelchair body  2  through a simple operation. 
     Further, since the seat frame  7  can be fixed to the wheelchair body  2  in conjunction with operation of attaching the seat frame  7  to the wheelchair body  2 , a simple operation is achieved. 
     The foregoing embodiments are merely preferred examples in nature in all respects, and the scope of the present invention should not be interpreted in a limited manner. Further, variations and modifications of equivalents of the patent claims are intended to fall within the scope of the present invention. 
     As described hereinabove, a wheelchair according to the present invention can be used in cases of, for example, carrying the wheelchair on a motor vehicle or the like.