A parallel movement mechanism including guide grooves and guide rollers and a vertical movement mechanism including cam grooves and cam rollers are interposed between a drive rod and a valve shaft of an air cylinder, and a valve seal of a valve plate is moved vertically toward and away from a valve seat surface to open and close the opening by moving the valve shaft in parallel to the valve seat surface by the parallel movement mechanism and moving the same vertically with respect to the valve seat surface by the vertical movement mechanism.