To always maintain a plane of a polishing surface, and simply, easily and quickly replace the polishing surface many times according to abrasion of the polishing surface by stretching it on a plane by placing sandpaper on an upper surface of a hard plane body.

A grinding wheel has a synthetic resin rectangular hexahedral hard plane body 10 and a soft synthetic resin elastic plate 20 which is adhered to its upper surface and has the same area. Sandpaper 30 is placed on the elastic plate 20, and when its excess both ends are sandwiched between the hard plane body 10 and a presser plate 40 are fastened by screw-fitting a butterfly nut 60 through a washer 50, the sandpaper 30 is stretched in a plane shape on the eleastic plate 20. A cutter is polished on this sandpaper 30.