PURPOSE: To simultaneously cause a mechanical grinding action and discharging and electrolytic grinding actions, to increase a grinding speed and to improve the workability of the material to be ground by metal-plating the surface of a grindstone.

CONSTITUTION: The surface of a grindstone part A is subjected to metal plating, electrified at 3 - 25V, in 0.1 - 5A so that one face B thereof becomes positive or negative and the other face C negative or positive and a tip discharging is caused at metal plating grind point E, F. Simultaneously therewith electrolysis is caused in the space connecting E point and F point via a grinding liquid. On the other hand, the material D to be ground is mechanically ground by this grindstone part A. Consequently, the material D to be ground can be ground with good efficiency by the synergism of this mechanical action and discharging and electrolytic grinding actions.