To solve the problem that when a semiarc shape is imparted to a barrel part of a seaming needle material 31, the seaming needle material can not be supported on groove parts 33 of a turret 32.

A semiarc shape is imparted to the seaming needle material 13 which is arranged with a sharp needle tip part 2 at a tip part of the barrel part 3. The seaming needle material 13 is constituted so that a base end part 4 is exposed between long size soft materials 14a, 14b, is set orthogonal to the longitudinal direction of the long size soft materials 14a, 14b, and plural seaming needle materials 13 are arranged/held at a prescribed interval. The long size soft materials 14a, 14b are intermittently transferred along the long size soft materials 14a, 14b. The base end part 4 of the seaming needle material 13 is subjected to laser machining at a first prescribed position B, a prepared hole 16 is pierced. At a second prescribed position C, by boring the prepared hole 16, a mounting hole part 5 is formed. A seaming yarn 6 is inserted into the mounting hole 5, caulking the mounting hole 5, the seaming yarn 6 is caulked. The boring is conducted by reaming.