To automatically polish a roll at constant speed under constant pressure without relying on manpower by reciprocating a polishing bar by normal rotation-reverse rotation of a driving motor through a rack-and-pinion by pressing it down to the roll by pressure of a spring.

A polishing bar 4 is guided by a slider 7, and is vertically pushed to rolls 12 and 13, and pressure is imparted by a spring 5. Pressure of the polishing bar 4 can be adjusted by an adjusting handle 6 by using a slider 8 as a guide. When the polishing bar 4 is reciprocated to surfaces of the rolls 12 and 13, it is performed by guiding normal rotation-reverse rotation of a driving motor 11 by a slider 9 through a rack-and-pinion 10. The normal rotation-reverse rotation of the driving motor 11 are switched to/from each other by a limit switch. Therefore, the roll can be automatically polished at constant speed under constant pressure without relying on manpower.