The invention provides a fastening method and a fastening tool which can stably fasten a nut to a bolt securely and with a small dispersion at a desired axial force. A fastened member is fastened by inserting a bolt to the fastened member, thereafter temporarily fastening a nut and the bolt, pulling a leading end of a shaft portion of the bolt in an axial direction of the bolt, rotating the nut so as to screw into the bolt while elastically deforming the bolt so as to generate an axial force, and thereafter canceling the pulling of the bolt.