PURPOSE: To lengthen life of an incandescent lamp with a rush current decreased by delaying timing to which a trigger is applied when the lamp starts lighting than normal lighting time with a control circuit controlling a trigger circuit provided.

CONSTITUTION: Output of a trigger circuit 13 is connected to the base of a transistor 17, and transistors 17 and 16 are cascade connected in parallel to a condenser 3. And condensers 22 and 23 are similarly cascade connected in parallel. A half-bridge circuit is formed with one end of the primary winding 20A of an output transformer connected to the middle point between transistors 16 and 17, and the another end connected to the middle point between condensers 22 and 23. A prolonged life of an incandescent lamp can be obtained as a rush current is decreased with a flowing time of current IL shortened by making a trigger to be applied in timing Tb with timing to which the trigger is applied to be delayed by time T with the control circuit 13.