An inductor for performing a chopper operation by turning on or off a first switching element MOSFET Q1 and obtaining an increased voltage is arranged on the secondary side of a transformer 112 and on the basis of the turn ratio of the transformer 112, a high voltage at the time of stable lighting can be obtained from a DC power source 111 at a low voltage Vin. Further, when the on-duties of the first and second switching elements MOSFET Q1 and Q2 constituting an inverter circuit are made almost similar, the timings of application of the power to both ends of a lamp 144 can be made similar, so that the life span of the lamp can be improved.