To provide a light-weight electronic ballast for a high-pressure discharge lamp, having small heat loss and an improved power factor, capable of reducing the start time and a restart time, and hardly affected by the variation of a power voltage.

This ballast is composed of a filter circuit 1 and a rectifying circuit 2 for smoothing A.C. power; a switching power circuit 3 for converting the pulsating power provided by the circuits into a D.C. power source stable with respect to power voltage variation and load variation; a soft start circuit 5 for preventing rush current, due to a high-capacity smoothing capacitor 4 connected to the load side of the switching power circuit; a heat-frequency oscillator for lighting a high-pressure lamp 11 with high frequency; a high-frequency drive circuit 7 for carrying out the switching derive of a gate by using a high-frequency signal generated using the high-frequency oscillator as a driver signal; an isolator 8 for isolating the driver signal; and a power amplifying circuit 9 for amplifying the power of the isolated driver signal.