A discharge lamp illumination circuit 1 has a DC-AC conversion circuit 3, which effects DC-AC conversion and boosting upon receipt of a DC input, and a starter circuit 4. Power output from the DC-AC conversion circuit 3 is controlled by means of control means 6. The DC-AC conversion circuit 3 has an AC conversion transformer 7; a plurality of switching elements 5H and 5L; and a resonance capacitor 8. The switching elements are activated by the control means 6, thereby causing serial resonance between the resonance capacitor 8 and a leakage inductance component of the AC conversion transformer 7, or between the resonance capacitor 8 and an inductance component 9 connected to the resonance capacitor 8. Provided that a resonance frequency achieved during an extinction period of the discharge lamp 10 is denoted as f1, the operating frequency is first regulated to a frequency level deviating from f1 and then gradually reduced so as to approach f1 in connection with a no-load voltage which is applied to the discharge lamp before illuminating.