After a DC voltage outputted from a rectifying circuit 2 is smoothed by a smoothing capacitor 3, transistors 4 and 5 are turned ON/OFF so as to convert the smoothed DC voltage into high frequency power. This high frequency power is supplied via a second resonant circuit 22 to a load circuit 23 and a first resonant circuit 17, and a high frequency voltage is superimposed on the output of the rectifying circuit 2 from the first resonant circuit 17.