A high-frequency high-voltage power supply is described, in which a high-frequency high-voltage is generated with the aid of L-C oscillation on the high-voltage side without making use of high-frequency primary power supply and a high-frequency high-voltage converter. Among two D.C. high voltage power supplies A and B, a negative output terminal of one power supply A and a positive output terminal of the other power supply B are connected together and then connected to one of high-frequency high-voltage output terminals, tank capacitors having a sufficiently large electrostatic capacitance Co as compared to an electrostatic capacitance C 1 of a load are connected between the positive and negative output terminals of the respective ones of said D.C. high-voltage power supplies A and B, one end of a first combination of a first thyristor and a first rectifier connected in an anti-parallel relationship to each other is connected to the positive output terminal of said D.C. high voltage power supply A with such direction of conduction that the anode of said first thyristor is connected to said positive output terminal, one end of a second combination of a second thyristor and a second rectifier connected in an anti-parallel relationship to each other is connected to the negative output terminal of said D.C. high voltage power supply with such direction of combination that the cathode of said ' second thyristor is connected to said negative output terminal, the other ends of said first combination and said second combination are connected with each other and then connected to the other of said high-frequency high-voltage output terminals by the intermediary of a resonant inductance, further there is provided a control device for feeding high-frequency current pulses alternately to the gates of the respective thyristors to turn on the corresponding thyristors alternately, and a capacitive load is connected between said respective high-frequency high-voltage output terminals.