PURPOSE: To improve the reliability of caulking by fixing preliminarily a rivet material by caulking to a base metal, inserting a material to be caulked onto the rivet material and caulking simultaneously the materials from both sides thereby eliminating the chipping down of the rivet material and preventing the decrease in the strength thereof, etc.

CONSTITUTION: A hole to be inserted with the rivet material 2 is formed to the base metal 1 by piercing. The rivet material 2 is inserted into the hole and is preliminarily caulked and fixed to the metal 1. One end of the material 2 is chamfered. The material 3 to be caulked is simultaneously caulked to the chamfered material 2 from both sides so that the metal 1 and the material 3 are joined by the material 2.