According to the present invention, to drive a magnetron, a pulse voltage is applied to the gate electrode of a field effect transistor to make the field effect transistor conductive, so that a voltage stored in a storage condenser is discharged through the primary winding of a pulse transformer and the drain electrode-the source electrode of the field effect transistor. This discharge causes the voltage generated at the primary winding of the pulse transformer to be induced at the secondary winding of the pulse transformer. Thus, the magnetron connected to the secondary winding of the pulse transformer is driven.