To provide a lighting method of a light source device, in which energy injection by laser irradiation is carried out by eliminating an effect of deposits on the inner face of a discharge container and high luminance lamp discharge is immediately achieved.

The lighting method of a light source device has a discharge lamp, a reflecting mirror to reflect light emitted from this discharge lamp, an irradiation optical system which emits the light reflected by the reflecting mirror on an irradiation object, one or more laser oscillators which emit laser beams on the discharge lamp, and a discharge starting means which starts discharge. The method comprises a first stage in which laser beams from a first laser oscillator is emitted on the discharge container and deposits adhering to the inner face of the discharge lamp is removed, a second stage in which discharge is started into the discharge container by the discharge starting means, and a third stage in which laser beams from a second laser oscillator are condensed into the discharge container.