Clamping method and clamping device

A clamping method comprising:

• a step of applying a predetermined first pressure to a plurality of members, which are superposed on each other, with a first support portion disposed on one surface side of the plurality of members and a second support portion disposed on a second surface side of the plurality of members to sandwich the plurality of members;
• a step of forming a through hole in the plurality of members with a cutting tool in a state where the predetermined first pressure is applied;
• a step of applying a predetermined second pressure lower than the predetermined first pressure to the plurality of members with the first support portion and the second support portion to sandwich the plurality of members after the through hole is formed;
• and
• a step of fixing a fastening part inserted through the through hole to the plurality of members with a fastening device in a state where the predetermined second pressure is applied to the plurality of members,
• wherein an amount of the predetermined second pressure is maintained to be uniform.