PURPOSE: To strongly join a thin metallic sheet by the device of simple structure by making the die main body a collet chuck type in case of deforming plural overlapped thin metallic sheets by swaging with a punch and die.

CONSTITUTION: Two sheets of thin metallic sheets 1a, 1b are pressed by a punch 3 in the overlapping state and pushed to the die main body 4 which is composed of the metal material elastically deformable and provides plural bottomed grooves 7. The pressure receiving part of the thin metal sheets 1a, 1b is pushed into a die hole 2 by forming a bottomed cylindrical projecting part 8 by bulging the pressure receiving part in the pressing direction by the increase of the pushing stroke of the punch 3. The lower face of this projecting part 8 stands still by being pressed to the still pressure receiving face 5 formed at the upper end of an axial pressure receiving part 6. The projecting part 8 is bulged in the radial direction of the die hole 2 with reducing the lamination thickness and the thin metal sheets 1a, 1b are strongly joined by swaging. In the finishing period of the joining motion, the bottomed groove 7 of the die main body 4 opens in the radial direction of the die hole 2 by the bulging of the projection part 8.