It is an object to obtain a light source device and a projection type display device in which a fragment can be completely enclosed therein even if a discharge lamp bursts during lighting. During normal lighting of a discharge lamp (1), an internal space of a light source device (10) and an external space are spatially connected to each other through a vent hole (43) formed on a cutoff valve mechanism (45) and a vent hole (100) formed on a concave reflecting mirror (4). Cooling air is introduced and discharged between the internal space and the external space so that the discharge lamp (1) is cooled down. When the discharge lamp (1) bursts during lighting for some reason, a very strong impulsive pressure wave is generated in a moment of the burst. The pressure wave presses a movable valve (41) provided in the cutoff valve mechanism (45) through the vent hole (100). By the pressing carried out with the pressure wave, the movable valve (41) is pushed up in a direction of an arrow (K1), thereby closing the vent hole (43).