To perform easily both of the regulation and stabilization of a discharge lamp.

An inverter circuit 3 is connected to a chopper circuit 2 and drives a discharge lamp 4. A circuit 21 is installed to generate intermittently square wave pulse at a frequency sufficiently lower than on-off frequency of a transistor Q3 of the chopper circuit 2. The pulse actuates the chopper circuit 2 intermittently to achieve the regulation of the discharge lamp 4. The electric current in the discharge lamp 4 is stabilized by the detection of the current in the discharge lamp 4 and control of on-time duration of the transistor Q3 for chopper. PWM pulse for on-off of the transistor Q3 for chopper is generated by synchronizing with on-off of transistors Q1 and Q2 of the inverter circuit 3.