To provide a lighting device for a discharge lamp which prevents shortening the service life of a discharge lamp.

The lighting device for a discharge lamp comprises a first and second switching elements which are alternately on/off controlled at high frequency, a third and fourth switching elements which are connected in parallel with the first and second switching elements and are alternately on/off controlled at a frequency lower than the frequency at which the first and second switching elements are controlled, a load circuit 14 including at least a lamp, a DC power source 111, a power conversion circuit which supplies the voltage of the DC power source 111 to a primary side and outputs a boosting voltage corresponding to the winding number ratio of a transformer to the secondary side to rectify the boosting voltage based on the on/off operation of the first switching element or the second switching element, a smoothing capacitor 12 for smoothing the output of the power conversion circuit, and a power supplying means which supplies the power supplied from the smoothing capacitor 12 to the first and second switching elements connected in series and the third and fourth switching elements connected in series.

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