An image forming apparatus includes an image bearing member, a transfer member, and a power supply unit that outputs a voltage to the transfer member. The power supply unit includes a first voltage generation circuit that includes a piezoelectric transformer driven at a drive frequency within a predetermined frequency area to output a first voltage having a predetermined polarity, and a second voltage generation circuit that outputs a second voltage with a polarity opposite to the predetermined polarity. In addition, a control unit controls the power supply unit to output a superposed voltage as a voltage having the predetermined polarity and corresponding to a voltage output from the piezoelectric transformer by driving the piezoelectric transformer at a driven frequency out of range of the predetermined frequency area, with the superposed voltage being a voltage in which the first voltage and the second voltage are superposed.