PURPOSE: To shorten the time of grinding with an electroformed grindstone, by prescribing the shape of the front end of the grindstone holder of a cup wheel and distributing abrasive grains in a high density on only a region of the front end of the holder.

CONSTITUTION: The surface of the front end 4a of a holder 4 is convexly curved with a uniform curvature. Abrasive grains are distributed in a high density in a metallic binder on the top region of the front end 4a to manufacture an electroformed grindstone 5. The central angle θ corresponding to the top region of the front end 4a, on which the abrasive grains are distributed, is set at about 90W120°. As a result, the electroformed grindstone is very firmly held.