PURPOSE: To prevent the edge from crack due to the groove, by polishing the bottom between each edge in the edge wave direction after setting the hot saw blade.

CONSTITUTION: Untill final setting of a hot saw blade 3, a polishing tool 17 supporting board 13 is displaced upwardly along the side of an elevating arm 5. At the final setting, the supporting board 13 is lowered to set at the bottom polishing position between the edges 3 through said tool 17 then said tool 17 is rotated together with a setting grindstone 7 through pulleys 12, 15 and a belt 16. Consequently the bottom section between the edges 3a finally set by the grindstone 7 is polished. A groove is produced in the bottom section between the edges 3a perpendicularly with the groove in the direction of the thickness provided near the tip section of the edge 3a to suppress the crack of the edge.