To provide a device to make electrolytic in-process dressing grinding using a cup-shaped grinding wheel as a grinding wheel, with which it is possible to produce a precise processed surface in the shape and surface roughness by generating a requisite and sufficient electrolytic dressing reaction between the grinding wheel as positive electrode and a negative electrode.

A cup-shaped grinding wheel 1 as a grinding wheel consists of a core 1a and an abrasive grain layer 1b, and the processing surface of the layer 1b is arranged so that the composition of a binder has a higher electrolitic rate in a position nearer the center A of the grinding wheel shaft, where the electrolytic dressing reaction is a lower rate in position nearer a grinding wheel periphery B. A uniform electrolytic dressing can be made over the whole surface of the grinding wheel, by improving the electrolytic rate in the vicinity of the shaft center of the wheel 1 where the electrolytic dressing reaction is insufficient.