PURPOSE: To prevent the generation of uneven luminance by connecting an electric discharge lamp to both the ends of a lamp lighting DC power supply through a series circuit consisting of a 1st resistor and a transistor(TR) and connecting 2nd and 3rd resistors and a controlling power supply to the lamp.

CONSTITUTION: The electric discharge lamp L is connected to both the ends of the lamp lighting DC power supply E through the 1st resistor R1 and the TR Q and the controlling power supply Ec for biasing the TR Q is connected between the node of the 1st resistor R1 and the power supply E and the base of the TR Q through the 2nd resistor R2. The 3rd resistor R3 is connected between the node of the TR Q and the lamp L and the base of the TR Q. Thereby a lamp current can be varied in accordance with the lamp voltage of the lamp L by feeding back the lamp voltage to the base of the TR Q through the 2nd and 3rd resistors R2, R3.