To accurately regulate output of a high-frequency power with a simple configuration. A high-frequency power supply circuit includes: a basic drive square wave generation circuit unit (5) for generating a basic drive square wave having an output frequency; a differential signal generation circuit unit (9) for generating a front edge differential signal of the basic drive square wave; a vibrator circuit unit (15) having a square wave signal generator (10) for outputting a square wave signal having a signal width within a period corresponding to a half cycle of the output frequency upon input of a trigger signal from outside and signal width control circuits (11, 12) varying/controlling the signal width of the square wave signal according to the control signal; and a switching amplification circuit unit (6) for amplifying the amplification source signal based on the output signal from the vibrator circuit unit (15). The front edge differential signal generated by the differential signal generation circuit unit (9) is made to be a trigger signal in the vibrator circuit unit (15).