To provide a power unit used for a lifting device which makes a wheelchair or the like ascend and descend to avoid a sudden ascent, descent and stop of a platform, to relax an impact given to a passenger in a wheelchair or the like on the platform, and to improve safety and reliability.

The power unit is used for the lifting device which drives the platform for up-and-down movement between a descent position and a position on a vehicle floor surface by rotating a parallel link by a double-acting hydraulic cylinder 20. The power unit has a hydraulic circuit and a sensor means. The hydraulic circuit has first, second, and third electromagnetic switching valves B1, B2, B3, first and second throttle valves 71, 72, and a float control valve FC. The sensor means detects that the platform has reached a point close to the descent position and a point close to the position on the vehicle floor surface. For a section from the descent position of the platform to its proximity point and a section from the position on the vehicle floor surface to its proximity point, it is so configured that the first and the second electromagnetic switching valves B1, B2 are turned off so as to reduce the flow rate of the operating fluid with the throttle valves.