A light source that prevents broken pieces from dispersing to the outside without increasing the number of components while efficiently cooling a light-emitting tube is provided. The light source (10) has: a light-emitting tube (11) having a light-emitting portion (111) where light beam is emitted by electric discharge between electrodes and a sealing portion (112) provided on both sides of the light-emitting portion (111); a reflector (12) that reflects the light beam emitted by the light-emitting tube (11) forward after aligning in a predetermined direction; a cover (16) covering a light-irradiation opening of the reflector (12) and having an opening for irradiating the light beam reflected by the reflector (12), the cover having a heat-radiation fin (162) on the outside thereof and being made of a heat-conductive material to absorb the heat from the light-emitting tube (11), the absorbed heat being conducted to the heat-radiation fin (162); and a transparent member (14) that covers the opening of the cover (16).