When a molded portion of a weather strip is molded, a slit, from which a core body is taken out, is formed in a mounting base portion thereof. Also, plural blocking pieces are provided at predetermined intervals along the slit. Each of the blocking pieces has a base piece portion formed in such a way as to extend from a mounting-face side of the mounting base portion, and also has an insertion portion, which is integrally formed with the base piece portion, and a lock portion to be locked on an inner surface of the mounting base portion. After the core body is taken out of a molded portion precursor, the base piece portion of each of the blocking pieces is bent around a part thereof continuously connected to the mounting base portion, so that the insertion portion is fitted into the slit, and that the lock portion is locked on the inner surface of the molded portion precursor, which faces a hollow portion. Thus, the molded portion is obtained.