A charger (200) electrically charges a main battery via (10) an electric power conversion path extending through an isolation transformer (260) and providing electrical isolation between an external power supply (400) and the main battery (10) when first and second relays (RL1, RL2) are turned off and a relay (RL3) is turned on. In contrast, the charger (200) electrically charges the main battery (10) via an electric power conversion path bypassing the isolation transformer (260) and providing electrical connection between the external power supply (400) and the main battery (10) when the first and second relays (RL1, RL2) are turned on and the third relay (RL3) is turned off. The charger (200) can thus selectively apply employing the isolation transformer (260) to ensure electrical isolation in externally electrically charging the battery, and bypassing the isolation transformer (260) to give priority to high efficiency in externally electrically charging the battery, as the relays (RL1-RL3) are turned on/off as controlled.