PURPOSE: To deform the space part of a polishing belt freely along the surface to be polished to polish the curved surface smoothly by forming a polishing tool with a polishing belt, of which polishing surface is directed outward and which can be deformed freely, and a holding body for stretching the polishing belt between parts with a space.

CONSTITUTION: The inner surface of an endless polishing belt 3, of which polishing surface is directed outward and which can be deformed freely, is stretched to both end directions of the belt 3 with a space by both end parts 51, 51 of a holding body 2, which is obtained by elastically deforming a flat plate into an arch, to form a polishing tool 1. At this stage, a space part 4 of the polishing belt 3, which does not abut on the holding body 2, namely, a part corresponding to a chord opposite to the inferior arch of the arch is deformed inward with the outward pushing of the polishing surface. Consequently, when the space part 4 of the polishing tool 1 is pushed to the surface to be polished of the material to be polished and while the polishing tool 1 is reciprocated, since the polishing surface of the polishing belt 3 is deformed and moved continuously along the surface to be polished, the surface to be polished is polished to the smooth curved surface.