Abstract: Base current is supplied from a base driving circuit to bases of paired inverter transistors through a transistor, and an inverter circuit oscillates at a rated output. When the operation of an electric discharge lamp becomes abnormal, an IC-ed control circuit is rendered operative responsive to output of an abnormality detecting circuit to turn the transistor ON and a transistor OFF, and the operation of inverter circuit is thus stopped. A capacitor in an auxiliary power source is charged by output of the base driving circuit and the control circuit is driven responsive to output of auxiliary power source when the inverter circuit is left inoperative.