The present invention intends to reduce standby power consumption in a multi-function printer which can be connected to an external device. The multi-function printer has user setting information 11b which can be changed by a user and in a power saving mode, a power supply unit 3 interrupts a power supply to a modem 14, a scanner 15, a printer 16 and a back light of a display unit 17 and the like, and also interrupts a power supply to an external interface unit 2 on the basis of the user setting information 11b. On the basis of detection results of connection detection units 21d and 22d for detecting the connecting state to a PC 102, the user setting information 11b is automatically changed so that the power supply to the external interface unit 2 in the subsequent power saving mode may not be interrupted. During connection to the PC, a changing operation of the user setting information 11b by the user is restricted.