A semiconductor switch circuit is connected to a primary winding of a transformer having a secondary winding connected to a load. The semiconductor switch circuit has switches controlled by PWM to provide a controlled constant current. In the inventive inverter, constant current control is performed by PWM operation of the switches of the semiconductor switch circuit. The inverter cuts off electricity to the control circuit when putting the control circuit into a standby state if a run-stop signal gains a logical stop-state. At the same time as the run-stop signal gaining the stop-state, switch drive signals enabling the switches of the semiconductor switch circuit are turned off. Thus, over-current can be prevented from flowing in the load when the control circuit is put into the standby state.