PURPOSE: To improve a straightening accuracy and to shorten the straightening time by providing the fixed holder and rotating holder in which the end part of the plate stock with torsion is inserted and by arranging the adjustor for adjusting the rotation angle on the rotating holder as well.

CONSTITUTION: The fixed holder 7 having the slits 7a, 7b in dissimilar dimension in provided for the guide rails 6a, 6b of an upper plate of a base 6 and the rotating holder 8 held to a bearing 9 is arranged in the opposition to the fixed holder 7 as well. The adjustor 12 having lock nuts 12a, 12b is arranged on the projecting part 10b of a rotating handle 10, besides. The straightening is performed by rotating the handle 10 by holding the other end by inserting it to the slit 8a of the rotating holder 8 as well as inserting one end of the plate stock 2 into one part of the slit of the holder 7. The shortening of the straightening time is enabled together with the improvement in the straightening accuracy due to the rotating angle being made constant by the adjustor 12.