A control device turns on a system relay and relays. A first boost converter rectifies an AC voltage supplied through a connector and a first power supply line. Further, the boost converter responds to a signal from the control device to boost the rectified voltage, and outputs the boosted voltage to a second power supply line. A second boost converter receives a voltage from the second power supply line to convert the voltage in accordance with a signal from the control device for output to a third power supply line. Since the system relay and one relay are both turned on, first and second batteries are connected in parallel to the third power supply line and a ground line. The first and second batteries are thereby charged.