When a press-in part 81 is pressed-in to a press-in hole 93, a vertex of the press-in part 81 deformed to a form along the inner surface of the press-in hole 93 comes into contact with the inner surface of the press-in hole 93 and a press-in force when the press-in part 81 is inserted into the press-in hole 93 or a pull-out force when the press-in part 81 is pulled out from the press-in hole 93 is set in according with the length of an intersecting line that a surface on which the outer surface of the press-in part 81 comes into contact with the inner surface of the press-in hole 93 and a section intersecting orthogonally to the axial direction of the press-in part 81 intersect.