PURPOSE: To perform dimming without changing the color temperature so much by feeding electric power containing the high frequency to a high-pressure discharge lamp, and adjusting the content of the high frequency in a lamp current.

CONSTITUTION: A serial circuit of the secondary winding of a pulse transformer PT2 and a capacitor C2 is connected between both ends of a high-pressure discharge lamp L, and the output of a high-frequency generating circuit 6 is applied to the primary winding of the transformer PT2. The lamp current to the lamp L is superimposed with this high frequency on the output of a lighting power circuit 1. The output level of the circuit 6 is adjusted by a dimming controller 7, and the content of the amplitude of the high-frequency current to the amplitude of the output current of the circuit 1 is adjusted. The high frequency is superimposed on the output of the circuit 1, and it is fed to the lamp L for dimming.