PURPOSE: To prevent the invasion or adhesion of powder, grain, and the like into a gap in a shaft part by fitting an O-ring which comes into contact with the surface of the end surface of a valve box side bearing, at the time of opening/closing of a valve, and which is responsive to the movement of the shaft, to a circular ring of the valve box side bearing part.

CONSTITUTION: In a butterfly valve in which a valve body 2 which is closely connected to the end surface of a valve box 1, and which is closely adhered to the surface of a valve seat, at the time of closing a valve, is separated from the valve seat surface, at the time of opening of the valve, so as to be moved perpendicular to the end surface of the valve box 1, an end surface 8 of a valve-attached shaft cylinder 7, and an end surface 6 of a valve box-attached bearing part are arranged so as to be in contact with the surface. At the time, a slidable circular ring 10 is installed on an inner circumferential surface 12 of a valve box 1-attached inner bearing part 5, while an O-ring that can be in contact with the inner circumferential surface 12 of the valve box- attached inner bearing part 5, as well as on the end surface 8 of a valve body-attached bearing part, is provided on a groove 9 formed on one side of the circular ring 10. The sealing of gaps P, U in a shaft part generated by the position control of a valve shaft 3 is secured thereby.