When causing a power saving mode to return by inputting a return signal, power is supplied to a device to which suppliance of power has been cut off. In this case, a power-saving control CPLD is masked to cancel an uncertain signal generated in the device under an intermediate potential at which the voltage of a power-saving-time power cutoff device, which supplies power to the device, is gradually rising. Thus, an erroneous operation caused by the uncertain signal can be prevented. Further, when the voltage of the power-saving-time power cutoff device reaches an operation-guaranteeing voltage, the power-saving control CPLD reads the uncertain signal again. Thereby, intrinsic characteristics of the uncertain signal can be verified, and a secure return operation can be implemented.