PURPOSE: To secure cutting accuracy while performing cutting operations repeatedly by causing a centrifugal force to act on a machining fluid for the separation of unground abrasive grains from chips of a workpiece to be cut and from ground abrasive grains, and reusing the unground abrasive grains separated.

CONSTITUTION: A lid-equipped cylindrical container 13 is rotated at high speed so that an abrasive fluid is continuously fed from a tank 16 to a center portion through a feeder pipe 14 by a certain amount of flow by use of a pump 17. Since fine grains cause a centrifugal force that is smaller than their surface force, they overflow from the top of the container 13, are discharged into an overflow collecting container 15, and returned into the tank 16 through an abrasive-fluid return opening 18. As a result, a machining-fluid circulation system is formed, and only abrasive grains with large diameters are accumulated on the side face of the container 13, while chips and ground abrasive grains are accumulated in the machining fluid in the circulation system. The abrasive grains on the side face of the rotating container 13 are remixed with support oil and used for re-cutting.