PURPOSE: To improve the straightening of a pipe and to insert it into the through-hole of a fin by integrally connecting tip part of a guide rod and the other end part of the pipe and imparting the pipe tension.

CONSTITUTION: By operating a second driving cylinder 16, the guide rod 19 is lowered together with a guiding rod holding member 14 and inserted into the through-hole 22a in the fin 22. The guiding rod 19 is rotated by the operation of the driving motor 20, and a tapping screw 21 is screwed into the upper end part of a U-shaped pipe 18 and integrally connected by screwing. At the time of driving the holding member 14 toward an ascending side or a holding member 15 toward a lowering side by operating at least one side of a second driving cylinder 16 or a third driving cylinder 17, the tension to axial direction is applied to the straight pipe part 18b in the pipe 18 to correct the deformation. By operating a driving cylinder 12, a guiding body 11 is slid toward an upper direction and the straight pipe part 18b in the U-shaped pipe 18 is inserted into the through-hole 22a in the fin 22 while being guided with the guiding rod 19.