To optimally control to stabilize an exciting frequency by accurately detecting a resonance current waveform without affecting a resonance circuit.

This high voltage generating power source turns on and off the primary side of a power transformer 3 in high frequency, rectifies, and steps up the high frequency voltage of a secondary side and generates an ultra- high voltage. The power source is provided with a resonance current detector 6 connected to a resonance circuit having a stray capacitance of a secondary side of the power source and a compensating coil to detect a resonance current, a peak detector 7 for detecting the peak of the resonance waveform of the detected resonance current, an exciting frequency generator 8 for generating an exciting frequency of the on and off frequency, and an exciting frequency stabilizer 9 for controlling the resonance frequency generated from the generator 8 for stabilizing the exciting frequency of the peak detected by the peak detector circuit. Here, the exciting frequency is swept, the exciting frequency of the peak detected by the detector 7 is obtained and stabilized to the exciting frequency of the peak.