Malfunctions of a switching device included in a power factor corrector are reduced when an instantaneous voltage drop or an instantaneous power failure occurs. If the instantaneous voltage drop or the instantaneous power failure occurs in an AC power source while the power factor corrector is performing a power factor correction operation by boosting an input voltage, an instantaneous power failure controller turns off the switching device included in the power factor corrector so that the power factor correction operation stops. When the commercial power source recovers, too, the power factor corrector suspends the power factor correction operation.