PURPOSE: To perform a job for grinding operation so efficiently by stirring magnetic abrasive grains automatically during the operation, and feeding all these grains to a working part.

CONSTITUTION: When a workpiece 3 rotates at high speed and a cylindrical body 4 rotates at low speed in the opposite direction, a magnetic substance 4a of part of this cylindrical body 4 reached to the vicinity of a magnetic pole is magnetized so that a line of magnetic force is produced in a gap with the magnetic workpiece 3 or the magnetic substance 4a in a part of the opposed cylindrical body 4, and magnetic abrasive grains 5 are held along these magnetic lines of force, thereby grinding a surface of the workpiece 3. In this case, a magnetic substance part and a nonmagnetic substance part of the rotating cylindrical body 4 are alternately situated between magnetic poles 6, repeating magnetization and demagnetization, and the magnetic substance 4a, where the cylindrical body 4 is magnetized, is moved to the other spot in order, therefore the magnetic abrasive grains 5 are moved in the cylindrical body 4. Accordingly, these magnetic abrasive grains 5 are automatically stirred, thus all these grains 5 are fed to a working part of the workpiece 3.