An apparatus for lighting a discharge lamp is provided with an inverter circuit 3 for causing an input power supply 2 to generate the voltage required for a discharge lamp 1, a rectifying smoothing circuit 4 for rectifying and smoothing the output of the invertor circuit 3, a feedback control circuit 8 for computing the power required for the discharge lamp 1 so as to control the feedback control circuit 8 in the feedback mode, a polarity switching circuit 9 for switching the polarity of the rectified and smoothed output to apply the output to the discharge lamp 1 with a low-frequency square wave, and an ignitor 11 for superposing a high-voltage pulse on the discharge lamp 1 when the discharge lamp 1 is started. The apparatus therefor further includes an overcurrent control circuit 14 for detecting an overcurrent flowing into the discharge lamp 1 so as to make the polarity switching circuit 9 perform a high-frequency chopper operation together with a low-frequency operation for only an interval during which the overcurrent flows, so that the life of the discharge lamp is prolonged by suppressing the overcurrent flowing into the discharge lamp and preventing its electrodes from wearing.