A detector may be a device for detecting insulation decrease of an electric system included in a vehicle. An external terminal may be configured to be connectable with a terminal of a power supply cable connected to a power supply device. A power supply relay, which may be provided between the external terminal and a power line, may be controlled by a vehicle ECU to be in a closed state during external power supply from the electrically powered vehicle to the power supply device. When the insulation decrease of the electric system is detected by the detector, the vehicle ECU may control the power supply relay to come into an open state.