PURPOSE: To repair the damaged part of the roll surface simply in good workmanship without requiring mounting/dismantling works or stock of spare rolls by performing the necessary process due to machining, while the roll is rotated, at the stage where the damage remains not serious.

CONSTITUTION: In case wear/damage of a roll neck 1b is not serious, the cover 6b of a gear box 6 is removed, and a machining device 7 is installed on the oversurface of the gear box body 6a. A roll to be repaired 1a is rotated by a repairing driver device 8 at a certain sped, and the surface of the worn/ damaged part is subjected to machining made by the machining device 7, and a smooth curvature is accomplished which is in smooth continuity from the surrounding parts of the roll surface. Thus the worn/damaged part can be repaired simply without removing roll 1a from bearings 2, 3, which eliminates necessity for heavy labor such as mounting/dismantling the roll repaired and/or spare rolls nd also associated roll conveying work. Further the operating effectiveness can be enhanced greatly, and the burden for arranging labors to the repair works and the repair period be reduced/shortened to a large extent.