Butterfly valve seat ring and butterfly valve provided with same

A seat ring for a butterfly valve is mounted on an inner peripheral surface of an internal flow passage extending along the flow passage axis in a valve body of the butterfly valve, so that an outer peripheral edge surface of a valve element supported to be rotatable in the internal flow passage by a valve stem supported by the valve body abuts on the seat ring. The seat ring includes a ring body having a cylindrical shape and extending in the center axis direction, and the ring body is formed at positions opposite to each other in a radial direction of the ring body with a pair of through-holes for allowing the valve stem to pass through. On an outer peripheral surface of the ring body, arcuate projections extending in a circumferential direction are formed apart from the pair of through-holes.