PURPOSE: To improve the discharging performance for chips from a ground surface and supplying the grinding oil onto the ground surface by forming a chip discharging groove on a grindstone acting surface, in a casted-iron bond diamond or CBN grindstone.

CONSTITUTION: A chip discharging groove 12 is formed on a grindstone acting surface 11. Therefore, the chips formed on the contact surface between a rotary grindstone 1 and a ground member, namely on the ground surface are discharged immediately into the chip discharging groove 12. When the grindstone 1 revolves, and the chip discharging groove 12 passes through the ground surface, the chips accumulated in the chip discharging groove 12 are discharged outside, and the can be discharged continuously from the ground surface. Further, the grinding oil supplied during the grinding work flows into the chip discharging groove 12 formed on the grindstone acting surface, and a large quantity of grinding oil flows uniformly onto the ground surface, and the ground surface is sufficiently cooled, and the superior grinding is permitted.