To obtain a stable operation regardless of the conditions of the supply voltage and a load, even in an inverter circuit wherein a ballast capacitor is omitted.

An inverter circuit has a pair of switching elements 2, 3, a step up transformer 7 having an input winding 4, an output winding 5, and a feedback winding 6, and a resonance capacitor 9. The ends of the input winding 4 are connected to the switching elements 2, 3, respectively, and a center tap of the input winding 4 is connected to a power supply through a choke coil 11 and AC voltage is supplied to the output winding 5 by letting the switching elements 2, 3 conduct alternately. In such an inverter circuit, a damping member such as a short ring 13 is added to the input winding 4 side of the step up transformer 7 to lessen Q of an oscillator circuit of the inverter circuit.