To cope with a requirement for good current balancing of a plurality of discharge lamps.

A plurality of current balancing transformers 6a, 6b and 6c are provided to correspond to a plurality of discharge lamps 3a, 3b and 3c. Primary coils 7a, 7b and 7c of he transformers 6a, 6b and 6c are connected in series to the discharge lamps 3a, 3b and 3c. Secondary coils 8a, 8b and 8c of the transformers 6a, 6b and 6c are connected in series each other. One ends of the discharge lamps 3a, 3b and 3c are connected to an output conductor 2a or 2b of an AC power supply circuit 1 through a serial circuit of the primary coils and secondary coils.