PURPOSE: To save power consumption by using LC circuit and isolating the resonance frequency of LC circuit from the frequency of a power supply unto a proper value.

CONSTITUTION: A LC circuit 1, 2 is connected to a power supply 9, and a reso nance frequency of the circuit is isolated from that of the power supply 9 to a proper value. That means, the impedance on the LC circuit 1, 2 can cope with negative characteristics in discharge of a lamp 3. A bridge 8 rectifies it to obtain dc voltage, then a smoothing coil 6 and a smoothing capacitor 7 are used to obtain a direct current which contains less superimposed alternat ing component and supply it to the lamp. Because the resonance frequency of the LC circuit is isolated from the frequency of the power supply 9, the loop of the coil can have less turns is compliance with the frequency, thus power loss can be reduced.