The object of the invention is to realize highly efficient cooling by enhancing the heat transfer rate between optical parts and cooling air, and by simultaneously lowering the temperature of atmosphere around the optical parts. For this purpose, a first wind outlet for blowing a cooling wind is provided so as to allow the cooling wind to pass through optical parts, and furthermore, a second wind outlet for blowing another cooling wind so as to interfere with the cooling wind from the first wind outlet at the optical parts is provided at a location different from that of the first wind outlet.