A power supply apparatus includes a piezoelectric transformer which outputs a voltage, a voltage-controlled oscillator which controls the frequency of an output signal in accordance with an input control signal, a power supply voltage supply element which is driven by a signal output from the voltage-controlled oscillator and applies a power supply voltage to the piezoelectric transformer, and an output voltage stop circuit (118) which outputs a signal for stopping driving the piezoelectric transformer on the basis of a control signal (Vcont).