PURPOSE: To make both fixed and movable blades polishable with one grindstone, by making this stone into a sheet form as a whole, forming an abrasive grain layer on the surface, and installing a long hole on a center line in the longitudinal direction of the body, while installing an engaged part in the one end.

CONSTITUTION: In case of polishing a movable blade 13, when a height part (engaged part) 2 of a grindstone 1 is engaged with the hole part 2a installed in a fixed blade 12, an abrasive grain layer (ceramic coating layer) 3 formed on a surface of the stone 1 comes into contact with the movable blade 13. A screw 9 is pierced into a long hole 6 of the stone 1, a nut 5 is screwed therein, the stone 1 and the movable blade 13 are connected onto the fixed blade 12, and the movable blade 13 are reciprocated as pressing it with a spring 4, thus it is polished by the abrasive grain layer 3. Furthermore, when the fixed blade 12 is polished, if the height part 2 of the grindstone 1 is engaged with a hole part 2 of the movable blade 13, the abrasive grain layer 3 comes into contact with the fixed blade 12, and when the grindstone 1 is reciprocated together with the movable blade 13, the fixed blade 12 is polished by the abrasice grain layer 3.