A lighting device for an ac-lighting type ultra-high pressure mercury lamp includes: a stepdown chopper for converting dc voltage that is supplied from the outside to voltage of a prescribed level; a full-bridge switch circuit for generating either dc or ac voltage from the output voltage of the stepdown chopper and supplying the generated voltage to the ultra-high pressure mercury lamp; and a control circuit for controlling the full-bridge switch circuit such that, when extinguishing the lamp, a dc voltage is supplied over a prescribed time interval with a prescribed electrode of the ultra-high pressure mercury lamp as the anode.