A fastening pin has an enlarged head part, and a shaft part. The shaft part includes a large diameter section formed below the enlarged head part, a middle shaft section formed below the large diameter section, and a small diameter section extending from the middle shaft section to a leading end of the fastening pin. The large diameter section includes a round portion formed below the enlarged head part and a taper portion formed between the round portion and the middle shaft section. A diameter of the large diameter section at a side of the enlarged head part is larger than a diameter of the large diameter section at a side of the middle shaft section. The middle shaft section has a uniform diameter from a side of the large diameter section to a side of the small diameter section.