An image forming apparatus includes a high-voltage power supply having a
piezoelectric transformer. The power supply includes a positive output
voltage generation circuit and a negative output voltage generation
circuit. Each of the positive output voltage generation circuit and the
negative output voltage generation circuit includes a piezoelectric
transformer, a piezoelectric transformer driving circuit, an output
voltage detection circuit, and a drive control circuit for outputting a
control signal for controlling the piezoelectric transformer driving
circuit using a signal from the output voltage detection circuit and an
output voltage setting signal for setting an output voltage. The positive
output voltage generation circuit and the negative output voltage
generation circuit are simultaneously turned on when the output polarity
of the high-voltage power supply with a piezoelectric transformer is
switched.