Abstract: A resonance power circuit comprises: a transformer having a primary coil and a secondary coil; a driving power source connected to the primary coil; a single switching device for conducting an ON/OFF control of a current which flows through the primary coil; a resonance capacitor which cooperates with the primary coil for producing a series resonance to generate a voltage pulse when the switching device is in an OFF state; a detector connected to the secondary coil for detecting a high voltage output from the secondary coil; a control circuit for controlling an ON period of the switching device on the basis of the high voltage detected by the detector to control a peak level of the voltage pulse; a damper diode for allowing a reverse current to flow through the primary coil during a damper period; and a clamping circuit for clamping a voltage across both terminals of the resonance capacitor to a voltage of the driving power source during a period from an end of the damper period to a start of the ON period of