To discharge wasteful charges in a power supply promptly, without making a crew member unpleasant in an electric vehicle.

A control unit 30 controls the operation of a power supply unit 10 and a switching mechanism 62. The switching mechanism 62 makes a motor 16 in a connected state with an engine 12 or a generator 14, or even in a disconnected state with both the engine 12 and the generator 14. When unnecessarily charge is discharged, a sleeve 64 of the switching mechanism 62 is slid by an actuator 66 by the controller to connect the motor 16 to a ring 70 of a float. At the same time, an inverter circuit in the power supply unit 10 for generating and feeding three-phase AC to the motor 16 is controlled through the control unit 30. Then, unnecessary charge left in a capacitor of a power supply unit 10 at a stopping time or excessive charge in the battery is used for rotating the motor 16 through an inverter circuit and discharged.