An inflator for an air bag, includes, a tubular housing including a gas discharge portion, a first fixing member provided in an outer circumferential surface of the tubular housing for fixing the inflator to a vehicle, the first fixing member including a contacting surface fixed to the outer circumferential surface, and a non-contacting surface extending in a direction tangential to the outer circumferential surface from one end of the first fixing member without contacting the outer circumferential surface. The first fixing member has a rib that extends from the contacting surface to the non-contacting surface.