An assisting mechanism is made compact. SOLUTION: When a slope plate 20 configured to be rotatable with respect to a vehicle body is rotated upward (rotated leftward), a supplemental force of a vehicle that acts in a direction to reduce a force for rotating the slope plate 20. In the mechanism 60, one end is connected to the vehicle body near the rotation center side of the slope plate 20, and the other end is connected to the vehicle body at a position farther from the rotation center than the one end. , A linear member 64 provided with an elastic body 66, and a pulley 61 mounted midway between the rotation center and the free end of rotation of the slope plate 20. When the pulley 61 is rotated, the pulley 61 is caught at an intermediate position of the linear member 64, and tension is applied to the linear member 64 to elastically deform the elastic body 66. [Selection diagram] Fig. 10【課題】補力機構をコンパクト化する。【解決手段】車両ボディに対して回動可能に構成されたスロープ板２０を上回動（左回動）させる際、そのスロープ板２０を回動させる力を軽減する方向に働く車両の補力機構６０であって、一端部がスロープ板２０の回動中心側近傍の車両ボディに連結されており、他端部が一端部よりも回動中心から離れた位置で車両ボディに連結されており、弾性体６６を備える線状部材６４と、スロープ板２０の回動中心と回動自由端間の途中位置に取付けられたプーリ６１と、を備えており、スロープ板２０が下回動（右回動）する際、プーリ６１が線状部材６４の途中位置に掛かり、その線状部材６４に張力を加えて弾性体６６を弾性変形させる。【選択図】図１０
