To provide a power supply circuit for a discharge lamp capable of improving conversion efficiency of electric power even if a harmonics current suppression (PFC) circuit is utilized.

As a boosted voltage outputted from the harmonics current suppression (PFC) 3 which is necessary for lighting the discharge lamp 5 is adjusted so as to be lowered into a certain voltage after retaining for a prescribed period from the start of lighting, the electric power conversion efficiency of the whole power source circuit can be improved even if the harmonics current suppression 3 is utilized, since the time duration of a high voltage boosting ratio of the harmonics current suppression 3 is shortened, and the time duration of a high voltage depression ratio of an output stabilizing circuit 4 is shortened, when the lighting of the discharge lamp 5 starts.