A button mounting member (10) is equipped with a base (11, 71) and a columnar post (12, 52, 62, 72) formed to stand upright on the surface of the base (11, 71). The columnar post (12, 52, 62, 72) is equipped with a post
barrel part (18, 58, 68, 78) extending from the surface of the base (11, 71) and a triangular cone-shaped post top part (19, 59, 69, 79) extending from the post
barrel part (18, 58, 68, 78). The post top part (19, 59, 69, 79) is provided with three first inclined surfaces (13, 53, 63, 73) that form the three side surfaces of the triangular cone, and second inclined surfaces (14, 54, 64, 74) that are inclined toward the tip and are formed on
ridge parts (15, 55, 65, 75) between the adjacent first inclined surfaces (13, 53, 63, 73).