PURPOSE: To eliminate the through current for switching of a switch circuit by providing a voltage stacking capacitor and providing a diode between the base and the emitter of a voltage stacking transistor TR and connecting the base and the output by a resistance and providing the switch circuit between the base and the ground.

CONSTITUTION: The base of a voltage stacking TR 3 and the output of an output circuit 1 are connected by a resistance 11, and a timing generating circuit 5 detects the rise of the output voltage to turn off a switch circuit 4, and the base voltage rises to turn on the voltage stacking TR 3. The flyback voltage is stacked in this manner. At this time, the through current does not flow because the turning-on period of the voltage stacking TR 3 and that of the switch circuit 4 do not overlap. When the flyback operation is terminated, a voltage stacking capacitor 2 is charged. Since a reverse bias is applied between the base and the emitter of the voltage stacking TR 3 by a diode 10 simultaneously with this charging, the TR 3 is turned off, and the voltage stacking TR 3 and the switch circuit 4 are not simultaneously turned on, and the through current does not flow.