To retard apply of surge generating in switching of a multi-terminal inductor to an inverter lighting circuit of a fluorescent lamp by using a power thermistor or a surge absorbing element.

Light control of a fluorescent lamp 7 is performed by adjusting voltage applied to an inverter lighting circuit 6 by switching a switch 3 of a multi-terminal inductor 2 stepwise. Since surge is generated when the switch 3 of the multi-terminal inductor 2 is switched, retarding of the surge is made necessary. By using a power thermistor 4 or a surge absorbing element 5, the inverter lighting circuit can be protected from the surge.