The fastener includes: a first facing portion and a second facing portion disposed so as to face each other, ends of the first and second facing portions being connected through a curved portion; a screw-fixing portion provided in at least one of the first and second facing portions and allowing a screw to be fixed thereto; and a rotation-preventing protrusion provided in one of the first and second facing portions and protruding therefrom in a direction from the one toward the other of the first and second facing portions, the rotation-preventing protrusion being disposed in an area next to the screw-fixing portion opposite to the curved portion.