PURPOSE: To supply a voltage and an electric current with high precision and to improve picture quality by utilizing the capacitive performance of a corotron for control over the output frequency of an inverter, and forming a negative feedback closed loop and stabilizing its output.

CONSTITUTION: An output detecting circuit detects a load voltage and generates a detection output corresponding to the voltage. A clock generator 1 increases in frequency according to the detection output when the output voltage is higher than a reference value or decreases in frequency when the voltage is lower than the reference value. A counter 2, a ring counter 3, 2/3 period PWM circuits 4 and 5, etc., use the output of the clock generator 1 as an operation clock, so the inverter output frequency increases or decreases in proportion to the frequency of the clock generator 1. A corotron, on the other hand, is capacitive, so the output rises and falls with the frequency, and the output voltage, therefore, becomes stable by the negative feedback control of the closed loop, improving the picture quality.