To provide a rotary valve that can produce a smooth stream of an intake for a high-speed rotation, has high rigidity, a simple construction and an easy maintenance, and high productivity, and to provide a molding die and molding method thereof.

In an inner wall surface of a valve flow passage formed in a valve body, arc-shaped downward curves are formed on top and bottom wall surfaces, and recess-shaped curved surfaces are formed on right and left side wall surfaces, and reinforcement ribs for balancing resin amounts of top and bottom are formed on outer surfaces of top and bottom wall surfaces. The molding of the valve flow passage is divided into two harves, and insert dies 14 for opening and closing which linearly go into and come from cavities 12a, 13b formed by mold dies 10, 11 are used.

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