PURPOSE: To carry out the exchange of sleeves collectively for all straightener shafts, by installing the cylinder which can deliver the sleeve against the straightener shaft, and the transferrer for transferring the sleeve between the outer cylinder and the straightener shaft.

CONSTITUTION: The straightener shaft 6 is set to the minimum inter-roll pitch and the minimum roll gap, and the protuberance 12 of the shaft 6 is fitted to the gear coupling 52, and at the same time, the phase offset between the spline groove 15 in outer circumference of the drum 14 of the shaft 6 and the spline groove 38 in outer circumference of the outer cylinder 37 is corrected. Next, the outer cylinder 37 is pushed out of the support shaft 32 through the rack 39 so as to press the stopper ring 23 segmented into three with the tip of outer cylider 37; hereby, the ring 23 is pushed into resisting against the spring force of the dish type spring 26, and the tip of the ring 23 is parted from the outer end plane of the sleeve 16 which is hereby made freely detachable from the drum 14. Then, the cylinder 51 is extruded for fitting the swing arm 49 into the nut 20, and the cylinder 51 is pulled back so as to pull away the sleeve 16 from the drum 14 and fit it to the outer cylinder 37; after that, the outer cylinder 37 is retreated from the shaft 52 for pulling away the sleeve 16.