An air passage opening/closing system preventing extraneous materials from depositing on a windup shaft drive mechanism of a film-shaped member, provided with a case forming air passages through which blown air flows, a film-shaped member arranged in the case and opening and closing openings of the air passages, a fixing part fixing one end of the film-shaped member at a peripheral edge of the openings, a windup shaft connected to the other end of the film-shaped member and winding up and feeding out the film-shaped member, and a windup shaft drive mechanisms rotating the windup shaft and making it move over the openings in a direction away from and approaching the fixing part, the windup shaft and windup shaft drive mechanisms being arranged at an air flow upstream side of the openings, a blown air blocking part covering at least an air flow upstream side part of the windup shaft drive mechanisms being provided.