PURPOSE: To lower the distortion rate of a power current by connecting a choke coil and a capacitor in series in a bypass circuit and minimizing impedance regarding a third harmonic current.

CONSTITUTION: A tap 4 is taken out of the middle of a stabilizer 1 to install a bypass circuit 5 in parallel with an electric discharge lamp 3. The electric discharge lamp 3 is set at the input side and a power source 2 is set at the output side, and a choke coil L3 and a capacitor C are connected to the bypass circuit 5 in parallel. Then, the impedance of the bypass circuit 5 is minimized regarding a third harmonic current which flows through the power source 2 side so that the distortion rate of a current which flows through the power source 2 is made small.