To provide a highly efficient power generation system by the motion of a suspension of a vehicle.

A power generation device for an electric motor-driven vehicle provides electric power of high efficiency by rotating an electric motor 15 connected to this shaft, by rotating a hydraulic motor 14 under its hydraulic pressure by setting the flow direction of oil constant, by installing a pair of directionally inverse check valves 9 in a port of this cylinder, by vertically moving the piston of a hydraulic cylinder 1 in response to the vertical motion of the suspension, by connecting the rod of the hydraulic cylinder 1 to the suspension of the vehicle.