A control circuit provided for an inverter power source circuit (1, 2, 3, 4) for a high frequency heating apparatus, the inverter power source circuit being adapted to supply electric power to a magnetron of the high frequency heating apparatus, by full wave rectifying and converting an alternating current from an alternating current power source to a direct current output and converting the direct current output to a desired alternating current output via a switching element and adapted to apply the oscillation control signal (e) to drive the switching element, the control circuit is operable to generate the oscillation control signal (e) based on a PWM control signal and wherein by means of the oscillation control signal (e), a current waveform of the alternating current output can be approximated to a sinusoidal shape by generating an electric current at both sides of the current waveform of the alternating current output; the control circuit comprising: - a control reference voltage setting circuit configured to have as input signal the PWM control signal and a detected sense signal (h) configured to be output from a current transformer for detecting the alternating current output from the alternating current power source, - the control reference voltage setting circuit configured to output a reference voltage setting signal (α) used as a first input for the waveform shaping signal generator, - an input waveform adjusting circuit configured to adjust a peak portion of an input waveform, and configured to have as input a signal having the adjusted input waveform from a signal (g) output from the direct current output, - the input waveform adjusting circuit configured to output a peak adjustment signal used a second input to the waveform shaping signal generator, the waveform shaping signal generator being configured to output a waveform shaping signal (c) and - an oscillation control signal generating circuit configured to generate the oscillation control signal (e) based on the waveform shaping signal (c), and a triangular wave signal (f) from an oscillator. - a control reference voltage setting circuit configured to have as input signal the PWM control signal and a detected sense signal (h) configured to be output from a current transformer for detecting the alternating current output from the alternating current power source, - the control reference voltage setting circuit configured to output a reference voltage setting signal (α) used as a first input for the waveform shaping signal generator, - an input waveform adjusting circuit configured to adjust a peak portion of an input waveform, and configured to have as input a signal having the adjusted input waveform from a signal (g) output from the direct current output, - the input waveform adjusting circuit configured to output a peak adjustment signal used a second input to the waveform shaping signal generator, the waveform shaping signal generator being configured to output a waveform shaping signal (c) and - an oscillation control signal generating circuit configured to generate the oscillation control signal (e) based on the waveform shaping signal (c), and a triangular wave signal (f) from an oscillator.