An oscillator provided in a charging cable outputs a non-oscillating signal when the potential of a pilot signal is around V(1), and outputs an oscillating signal when the potential of the pilot signal is lowered to V(2). A pull-down resistance element provided in the plug-in hybrid vehicle is connected between a control pilot line and a vehicle earth, and changes the potential of the pilot signal from V(1) to V(2). A switch is connected in series between the pull-down resistance element and the vehicle earth. When the charging cable is connected to the vehicle, the switch is turned off and the pull-down resistance element is separated from the vehicle earth.