PURPOSE: To reduce the twist of a pipe and to prevent the pipe from causing ruggedness, crease, and flaw, etc. by relatively moving a mandrel in the reverse direction to the relative movement of an annular tool with respect to the pipe.

CONSTITUTION: A pipe 7 with a mandrel 6 inserted therein is inserted into a ring roll caliber D2, and a gear 9 beared at its outer surface by a housing is driven in the arrow 10 direction. Then the inner surface 13 provided eccentrically to the gear 9 moves eccentrically, and the center L of a ring roll 4 and the ring roll caliber D2 revolves with a radius LK around the center K of the outer circle of the housing and the gear 9. When the diameter of ring roll caliber D2 is selected close to the diameter at the position concerned at that time; the wall thickness of pipe is form rolled between the mandrel 6 and the caliber D2, and the mandrel 6 is bent to shift its center to M located at a distance from K. The wall thickness of pipe is also press reduced even at the calibers D1 or D2 by properly selecting the dimensions of calibers D1 or D2.