A light source apparatus having a housing including a mercury xenon lamp 3, a reflecting mirror 4, and a gas-blasting structure 5 including a plurality of spray ports for blasting an inert gas onto a reflecting surface of the reflecting mirror. The gas-blasting structure is positioned around an exit aperture of the reflecting mirror, and includes a supply port for receiving the inert gas from the outside. The spray ports are arranged to be off a line along a direction of the gas introduced through the supply port.