To provide a method and a structure for fastening a plate material, capable of fastening plate materials together without forming projections on the front and rear surfaces at the fastened parts.

A plate-like member 11 with a cylindrical projection 13 is disposed on one surface, and another plate-like member 12 with a countersink 14 is disposed on the other surface. The cylindrical projection 13 is inserted into the countersink 14 from the side opposite to the recess to spread the projection 13 along the recess of the countersink 14.