According to the present invention, there is provided a light source device having a reflector including a light source lamp and an opening for emitting light for reflecting light radiated from the light source lamp arranged within the reflector to emit the light from the opening, and a glass arranged ahead of the opening of the reflector inclinedly by a predetermined angle with respect to a plane perpendicular to the optical axis of light emitted from the reflector. According to the light source device, the light source lamp is prevented from temperature rise and consequent overheat caused by light reflected on the glass thereby to return into the reflector.