The power supply apparatus includes a first control part that controls a switching operation of a first converter, a second control part that controls a switching operation of a second converter, a zero crossing circuit that outputs a zero crossing signal of a voltage to be input; and a voltage supply part that supplies a DC voltage obtained by rectifying an output of an auxiliary coil of a transformer of the first converter to the first control part, the second control part, and the zero crossing circuit. When the first converter stops, the supply of the DC voltage to the second control part and the zero crossing circuit is stopped to reduce a power consumption.