The present invention comprises: a valve housing having a driving space formed therein and a moving passage part perforated in both surfaces thereof; a blade provided in the driving space, for opening and closing the moving passage part from the inside; a main shaft coupled to the rear surface of the blade; a vertical moving part which is formed beneath the valve housing, and in which the main shaft and a first piston, which moves vertically by pneumatic pressure, are connected to vertically move the blade; a horizontal moving part coupled to the lower part of the vertical moving part and provided with a vertical moving guide groove perforated vertically in both side surfaces; a horizontal moving unit having a second piston provided inside the horizontal moving part, a movement guide block formed beneath the second piston, and a cam roller formed at both sides of the movement guide block and passing through the vertical moving guide groove; and a main body bracket formed such that the vertical moving part and the horizontal moving part are accommodated beneath the valve housing, and having an opening and closing guide groove inclinedly formed in both side surfaces such that the cam roller, having passed through the vertical moving guide groove, is inserted so as to guide the fore and aft movement of the blade according to the vertical movement of the horizontal moving unit.