A first power storage portion stores power generated by a generator in a vehicle, and supplies power to a motor for starting an engine and an electric device in the vehicle. A second power storage portion is connected to the first power storage portion in parallel, and stores power generated by the generator, and supplies power to the electric device in the vehicle. The first power storage portion and the second power storage portion are connected each other in parallel. A first switch is inserted in a path between the first power storage portion and the second power storage portion. A diode is connected in parallel with the first switch such that a cathode side thereof is connected to the second power storage portion side. A second switch is provided between the path and the second power storage portion.