A power supply device is disclosed that outputs a voltage of a wider range with a single piezoelectric transformer. The power supply device includes a piezoelectric transformer 101 for applying an output voltage to a transfer member that transfers a toner image formed on an image bearing member onto a recording material. The power supply device further includes a generation unit 110 configured to generate a driving frequency for driving the piezoelectric transformer 101. A control unit 701 controls a spurious voltage by changing driving frequency characteristics of the power supply device in accordance with a target value of an output voltage Vout.