The present invention relates to a fastener and a fastening method for joining together two or more members including at least one complicate-shaped plate. A fastener comprises a cap nut (20) having a main body and a thin-walled portion (24) projecting from the main body, and a bolt (30) screwed into the cap nut (20). The cap nut (20) is fixed to a plate-like member (12) by inserting the thin-walled portion (24) into a through-hole (12a) of the plate-like member (12) and caulking the thin-walled portion (24).
