A diode is provided in a first supply route for the electric power from an AC adaptor, rectifies the current from the AC adaptor and, at the output side thereof, is connected to a second supply route for the electric power from an AC adaptor. A detecting unit is connected to the input side of the diode in the first supply route and, based on the voltage that is input from the first supply route, detects whether the AC adaptor is connected. A resistance control unit reduces the combined resistance between the ground and the input side of the diode when the temperature of the device, including the diode, is equal to or more than a predetermined temperature.