In a power supply apparatus including a plurality of power supply circuits, each of the power supply circuits has a piezoelectric transformer, a rectification element which rectifies and smoothes a voltage output from the piezoelectric transformer in accordance with a load and outputs the voltage, a voltage-controlled oscillator which controls the frequency of an output signal in accordance with an input control signal, and a power supply voltage supply element which is driven by a signal output from the voltage-controlled oscillator and supplies a power supply voltage to the piezoelectric transformer. One power supply circuit includes a resonance frequency change unit which is connected to the output side of the piezoelectric transformer. The resonance frequency change unit drives the piezoelectric transformer of the power supply circuit at a driving frequency which is different from the driving frequency of the piezoelectric transformer in another power supply circuit by shifting the peak of the resonance frequency.