To polish the plate surface of a saw plate 1 with excellent accuracy instantly by means of a strong polishing pressure.

An engagingly locking part 4 for blocking the shift movement of a saw plate 1 in relation to a bearing surface 2 by having the edge part of the saw plate 1 engagingly locked to the bearing surface 2 is provided after arranging the bearing surface 2 in the longitudinal direction and polishing body 5 such as a grinding wheel or the like in contact with the saw plate 1 supported on this bearing surface 2 is facingly installed in relation to the bearing surface 2. A bearing body 3 on which this bearing surface 2 is formed in relation to the polishing body 5 is composed in the length direction of the saw plate 1 with free relative movement thereto and by pressing this polishing body 5 on the plate surface of the saw plate 1 making relative movement to the polishing body 5, the plate surface of the saw plate 1 can be continuously polished in the length direction.