PURPOSE: To make a high voltage change over switching circuit unnecessary by using each pair of modulators, power amplifiers, highfrequency transformers, and voltage doubler half-wave rectifiers.

CONSTITUTION: A low-frequency high-voltage power supply is composed of a verylow-frequency oscillator, a carrier oscillator, positive and negative half- wave modulators, power amplifiers PA, high-frequency step-up transformers T, voltage doubler half-wave rectifier circuits and others to supply power via smoothing capacitor CO and the like. Further, said smoothing capacitor CO is connected between respective output terminals of said rectifier circuits via short-circuit prevention and waveform composition resistances R respectively, and a negative feedback circuit to a low-frequency amplifier A is also provided at said power supply. Thus, a high-voltage waveform having the same frequency as and being similar to those of said low-frequency oscillator output can be obtained between smoothing capacitor terminals.