A switching operation is performed on a switching element of a power-factor improving unit that includes a reactor. An output voltage of the power-factor improving unit is set to a load voltage by switching on and off the switching element based on a result of comparison between an input current and an input-current reference signal of a power-supply voltage waveform. A zero cross of an alternate-current power supply is detected, and the switching operation is performed on the switching element a predetermined number of times based on a detection of the zero cross.