A clamping method includes a step (S3) for applying, by a first support portion disposed on one surface side of a plurality of superposed members and a second support portion disposed on the other surface side of the plurality of members, a predetermined first pressure to the plurality of members, and sandwiching the plurality of members; a step (S4) for forming a through hole with respect to the plurality of members by a cutting tool with the first pressure; a step (S5) for applying a predetermined second pressure to the plurality of members after the through hole is formed, and sandwiching the plurality of members by the first and second support portions, the second pressure being lower than the first pressure; and a step (S6) for fixing a fastening part inserted into the through hole to the plurality of members by a riveting device with the second pressure applied.