To stabilize a current control in a power supply apparatus having a power factor improving means and further facilitate a power supply harmonic regulation. An input power supply (1) is converted to a DC voltage and then a boost chopper circuit (3) is used to provide a voltage for a load (4). At this moment, a switching element (3c) of the boost chopper circuit (3) is switched to make a short circuit via a boost choke coil (3a), thereby improving the power factor. At this moment, a control part (13), which controls the power supply apparatus, turns on or off the switching element (3c) in accordance with a result from comparing a detected input current from an input current detecting part (10) with a sinusoidal input current reference signal. In the meantime, the control part (13) switches the switching element (3c) a predetermined number of times from a zero cross detection by a power supply phase detecting circuit (5) in every half of the AC power supply period, and inhibits the switching element (3c) from being switched thereafter, whereby the number of times the switching element (3c) is switched in every half of the AC power supply period can be inhibited from varying.