PURPOSE: To preclude a switching circuit from variations of charging voltage caused by its opening delay in such a way that a ripple phase detecting circuit is provided for performing the charge to a high voltage capacitor at a settled position for ripples of its charging voltage.

CONSTITUTION: Control signals from a switching control circuit SC gives closure through a switching circuit SW to an neutral point of the primary winding L1 of a high voltage transformer HT, generation of high voltage on the output terminals of secondary windings L21, L22, start-up of charging through high voltage rectifiers HD1, HD2 to capacitors HC1, HC2. Its charged voltage is detected by resistors R21, R22, which are respectively guided into a comparator CM, upon achievement of a settled potential, the circuit SC gives opening through the circuit SW to the neutral point of the primary winding, to stop charging. In the meantime, a ripple phase detecting circuit PC controls the switching control circuit SC so that charge start-up timing can be a settled phase for ripples.