PURPOSE: To simultaneously polish the bottom face and side face of a recessed groove by fitting the polishing sheet in the same shape as the side face shape of a roller freely detachably to the side face of the roller.

CONSTITUTION: An end roller 15 is supported in a center support type and abrasive sheets 203, 206 are fitted freely detachably to both side faces of this end roller 15. Consequently, flat side faces can be polished by the abrasive sheets 203, 206 simultaneously with performing the polishing of a bottom face by a polishing belt in the polishing work of a recessed groove.