A grinding wheel that can rotate at high speed to grind flat plates is comprised of a thin conical grindstone fastened to the open end of a rotatable inverted cup, with the grinding edge projecting outwardly from and at an inclined angle with respect to the open end. The grindstone includes a cylindrical fitting part which is fastened to the inside of the cup and a conical grinding part formed by electroplating from a nickel plating solution in which super hard abrasive grains are dispersed. The grindstone can also be prepared by electrodepositing abrasive grains directly onto a flange formed at the open end of the cup.