The device comprises a first power supply 204 supplying electric power in the normal mode, a second power supply 203 supplying electric power in the power-saving mode, a first switching unit 211 switching between supplying and stopping the supply of electric power from an external power supply to the first power supply, a second switching unit 502 switching between supplying and stopping the supply of electric power outputted from the first power supply 204, a control unit controlling the first switching unit 211 and second switching unit 501 using electric power supplied from the second power supply. In the power-saving mode, the first switching unit stops the supply of electric power from the external power supply to the first power supply.