To provide a semiconductor manufacturing apparatus capable of effectively cooling a light shielding device in failures of air fluctuation occurring on light path, eliminating factors for producing defective device by the absence of illumination variance and uneven illumination caused by the air fluctuation for short period of time, improving operating rate of the apparatus, and decreasing operating cost of the apparatus.

A hollow shutter 10 for shading and projecting light from a source lamp 9 is effectively cooled from inside by supplying the internal hollow space of the shutter 10 with air for cooling which is temperature controlled by a cooler 16 and an air blower 17 respectively controlled by a cooler control section 18 and an air blower control section 19, thereby causing no air fluctuation in light path caused by cooling air. The blowing volume and temperature of the air for cooling is controlled according to the projection state, light shielding state, and retention time of the light shielding state, furthermore input power for the source lamp 9, and the like.