To provide a rivet of low cost without much labor in coupling, by providing axial bore having two different diameter parts, that is, a first part of small diameter extending from a lower end and a second part of large diameter extending from an upper end over a part of the bore.

A first die 15 comprises a base 16 and a projection 17. The projection 17 has an outside dimension similar to that of a first part 7 of an axial bore, and is inserted to the axial bore. The base 16 of the die 15 is brought into contact with a flange 6. The projection 17 is also inserted to a bore 22 of a second die 20. The bore 22 of the second die 20 has the same dimension as the first part 7 of the axial bore. The second die 20 comprises a contact surface 21 provided at a lower end 4 of a rivet. In this arrangement, as shown in arrows in Figure, as the first and second dies 15 and 20 are simultaneously moved so as to face to each other, a wall is crashed in a second part region of the axial bore by the compressive force acting on a wall of a pipe shape to form a gusset 24, whereby a workpiece 12 is held between the gusset 24 and the flange 6.