PURPOSE: To process many ceramic balls at one time by bringing free abrasive grains in contact with ceramic balls effectively by mounting a machining bath which contains suspension consisting of free abrasive grains dispersed in high molecular solution and ceramic balls and a stirrer which stirs suspension in the machining bath.

CONSTITUTION: When a stirring blade 12 is rotated, ceramic ball W which has a specific gravity smaller than that of metal ball is simply dispersed and floats in suspension 10 together with free abrasive grains. Particularly, projection section on the surface collides intensively with free abrasive grains and is ground to approach a true ball gradually. In this case, suspension 10 which contains free abrasive grains having comparatively large grain diameter is used, and it is changed over into suspension 10 which contains free abrasive grains having small grain diameter as the grinding process advances. Then, it is possible to approach ceramic balls W to true balls due to changes of number of contact and contact position of abrasive grains for ceramic ball W. Their surfaces become smooth. Thus it becomes possible to machine many ceramic balls W at one time.