PURPOSE: To increase a discharging condition detecting accuracy and to provide a discharge preventive circuit suitable for the discharging condition.

CONSTITUTION: A comparator COMP1 is driven by comparing a discharging detecting voltage V1 generated on a high-voltage output terminal of a secondary winding N2 of a transformer T1 at the time of discharging with a reference voltage VREF1. At every output from the comparator COMP1, oscillation of a PWM control circuit 2 is stopped through a diode D1. A comparator COMP2 is driven when the number of outputs from the comparator COMP1 reaches a specified one. Oscillation of the PWM control circuit 2 is stopped due to the output from the comparator COMP2 through a PWM shut-down circuit 1 and then output of a high-voltage power supply is stopped.