A resistor is connected to first and second terminals included in a vehicle inlet. To the first terminal, a control pilot line used for transmitting a pilot signal is connected. In the case where the vehicle inlet is not connected to a connector, a switch is turned off. A voltage generation circuit sets the potential of the second terminal to a potential higher than a vehicle earth potential. In the case where the vehicle inlet is not connected to the connector and the control pilot line is broken, the potential generated on the control pilot line is substantially equal to the earth potential level. Based on the potential of the control pilot line, a control unit detects a break.