PURPOSE: To maintain the shape precision of a worked member by carrying out the electrolytic in-process dressing grinding for maintaining the shape of a grinding tool by forming an electrode to an arcuate shape and the shape far reducing the opposed part toward the outer periphery of the grinding tool.

CONSTITUTION: An electrode 4 is formed to an arcuate shape whose opposed part reduces toward the outer periphery of a grinding tool 2. The electrode 4 thus formed is set to a spherical shape opposed to the grinding tool 2, and when the grinding tool 2 is swing-moved, electrolysis is applied by a switching device 7 only in the case where the rotary shaft 3 of the grinding tool 2 and the electrode and nearly coincide. Accordingly, the electrolytic in-process dressing grinding in which the shape of the grinding tool is maintained can be carried out, and the grinding work in which the shape precision of a worked member is maintained can be carried out.