An energy-saving control unit detects a supply of power to an image forming apparatus and performs an energy saving control of an external controller. A switching unit switches a start and a stop of supply of power to an onboard circuit of the external controller. Upon detecting the supply of power to the image forming apparatus, the energy-saving control unit sends a power control signal for instructing a start of the supply of power to the onboard circuit to the switching unit. Upon receiving the power control signal, the switching unit switches to the start of the supply of power to the onboard circuit.