For the acrylonitrile resins that may be used in the present invention, a resin, the main ingredient of which is polymerized acrylonitrile, is indicated, and generally, a copolymer of acrylonitrile and a small amount of butadiene, etc., as the rubber ingredient, and/or one kind or two or more kinds of acrylates and/or methacrylates such as methyl acrylate, methyl methacrylate or the like are used.