A battery state monitoring portion intermittently monitors the low voltage battery for supplying power to electrical components arranged in a vehicle while the power supply to the low voltage system load other than a +B load is stopped, a DCDC converter is stopped, and a +B power supply mode in which the vehicle cannot travel is set. A charging control portion starts up the DCDC converter and charges the low voltage battery with the power of a high voltage battery as a power source of the vehicle through the DCDC converter when the voltage of the low voltage battery becomes lower than or equal to a charging start voltage when the +B power supply mode is set. The present invention can be applied to a charging device of a battery of an electric vehicle.