A discharge lamp lighting circuit has a structure of a voltage resonance type including a transformer and a switching element to be provided on a primary side thereof as a DC—DC converting circuit for converting a DC input voltage into a desirable DC voltage. The lighting circuit further includes a control circuit serving to ON/OFF control the switching element, thereby controlling an output voltage Vout of the DC—DC converting circuit, and has a function of a current limitation related to the switching element. In the lighting circuit, if the output voltage Vout is raised, a current flowing to the switching element is limited to be decreased. Consequently, a voltage applied to the switching element can be suppressed, and furthermore, the winding ratio of the transformer does not need to be increased. Accordingly, it is possible to prevent an electrical efficiency from being deteriorated.