A reception unit sequentially receives input of voltage values indicating an AC input voltage from an AC power supply. A ROM stores a power control table in which a power control parameter corresponding to the AC power supply voltage is matched with each group of the voltage values indicating the same AC power supply voltage. A decision unit determines to which group the received voltage values belong among the plurality of groups, whenever the reception unit receives the input of the voltage value and decides the group, to which a predetermined number of voltage values belongs among the plurality of voltage values sequentially received by the reception unit, among the plurality of groups using the determination result. A power control unit controls power supply according to the power control parameter matched with the decided group.