PURPOSE: To center easily pipings and to improve accuracy in tack welding of the pipings by providing fixing pieces for pipings to one cylindrical inside surface of either of a cylindrical piping retainer or a cylindrical centering body and providing centering pieces to the other cylindrical inside surface.

CONSTITUTION: A piping retainer 11 is put on one piping 23 and is mated to bring the center of a centering body 13 to the bevel of the piping 23 and thereafter the retainer 11 is rotated to lift centering pieces 18 by tapers 20 to tighten the piping 23. Lock bolts 17 for piping provided at four points are turned and the piping 23 is fixed by fixing pieces 16 for piping while the pieces 18 are held lifted. The other piping 24 is inserted from the side of a piping retainer 12 and the bevel of the piping 24 is inserted to the center of the body 13. The retainer 12 is rotated to lift the pieces 18 by the tapers 20, then the piping 24 is tightened. The bolts 17 are turned to fix the piping 24 by the pieces 16. After the centers of the two pipings 23, 24 are matched, tack welding is performed through the window of the body 13.