PURPOSE: To greatly improve the productive capacity without fattening the edge portion, by adding a motion for chainging the roll gap of the stepped rolls, as the adjusting motion in the traverse direction agianst the rolling direction, correspondingly to the increment of the roll gap caused by th swing motion of the turning axis.

CONSTITUTION: The high point 38 is situated at the nearest position to the pipe axis, and rolls the pipe into thin wall; hereupon, the cross angle between ases of the roll shafts 2 is comparatively large, so that a comparatively large feed for the rolling is given. Just before the tail end of the materal arrives, the turning device 28 is driven, and the cross angle between the rolls is reduced by the movable flange 9 rotated by the turning device 28. By the rotation of the movable flange 9, the gear 19 turns the screw cylinder 17 which is unmovable in the direction within the movable flange 9; by the rotation of the screw cylinder 17, the roll chock 6 is moved toward the rolling line. Thus, the displacement of the high point 38 from the rolling line, being caused by th reduction of the cross angle between roll axes 2 can be corrected.