Discharge lamp electronic ballast includes DC-DC converter circuit for converting voltage of DC power supply to output DC power, inverter circuit for converting DC power into AC power to supply it to discharge lamp, output feedback control circuit for controlling DC-DC converter circuit, and inverter driving signal generator circuit for controlling inverter circuit. Ballast includes microcomputer having voltage detecting function for detecting voltage value of DC power supply, and ballast temperature detector circuit for detecting temperature of ballast. Microcomputer sets first time based on voltage value of DC power supply and detection result of ballast temperature detector circuit, and reduces power supplied to the discharge lamp if first time elapses from time point when lamp is started, thereby supplying lamp with power for stable operation.