PURPOSE: To make an installation small in size and to speed up a titled work by forming a pass which becomes narrower while undulating in bellows shape in the inner surface of an annular tool and working a long columnar body inserted in the tool into a spiral shape while moving the body relatively to the tool.

CONSTITUTION: A pipe 7 with a mandrel 6 inserted therein is penetrated into an eccentric ring roll 4 by a propelling device 14, and the working face of the caliber D2 of roll 4 is forcibly inserted onto the outer circumference of pipe 7 by supporting the pipe 7 by the calibers D1, D3 of supporting ring rolls 3, 5. At that time, when the caliber D2 of roll 4 is eccentrically rotated through the inner face 13 of a gear 9 supported by a housing 11, a part plastically press-deformed by the caliber D2 advances while moving in the circumferential direction of pipe 7, and the wall thickness of the whole circumference of pipe 7 is press-reduced into a spiral shape. In this way, the plastic working of a pipe is efficiently performed, and the size reduction of an installation and the speed up working are achieved.