A molding device for molding a molded portion of a weather strip has a lower mold, an upper mold, a first sliding mold, a second sliding mold, and a core mold. The core mold has a core body and a core holding portion. The core body comprises a molding part, and insertion parts, into which end parts of an extrusion portion are respectively inserted. The core holding portion extends from only a one-side part of the core body. Cutout portions are formed in parts in which the core holding portion is not present. Convex portions of the second sliding mold are fitted thereinto in what is called a zero-abutment state. Upon completion of molding, the second sliding mold is slid to thereby cause a molded portion to perform relative movement with respect to the core mold. Consequently, the core body can extremely easily be removed from the molded portion.