A rotary valve made of ceramics has edges at the junctions between a generally cylindrical outer periphery and opposite ends of a through hole. Each of the edges has a leading edge portion at which the valve starts opening and a leading edge portion at which the valve finishes closing. The leading edge portions are chamferred in such a way as to form part of surfaces of right circular cones whose vertexes are contained in an axis of rotation of the rotary valve and whose axes coincide with the center axis of the through hole.
