Abstract: A butterfly valve comprised of main body, a seating ring installed in the seating ring, and a disk shape valve member rotatably provided in the seating ring. The seating ring has an inside projecting ridge so that circumferential edges of vanes of the valve member come into contact with the side edges of the projecting ridge when the valve member is closed. The outer circumferential surface of the valve member is formed spherically as a whole so that machinery cutting of the surfaces of the valve member can easily be accomplished by a lathe. The seating ring has shaft supporting portions formed in concave surfaces so as to conform to the spherical surface of the valve member. Two vanes of the valve member are located at point-symmetrical positions with respect to shaft receptacles which are provided on the axis line of the valve member and extended tangentially with respect to the shaft receptacles.