PURPOSE: To reduce the extent of wear in an electrode, by applying an insulative, thin surface treatment layer to an outer circumferential surface of the electrode body, and having part of a film exposed in adjustment with machining conditions on a workpiece.

CONSTITUTION: An electrolyte passage 12 and a transverse outflow port 12a are installed in the electrode body 11 formed with an aluminum alloy or the like. An starting hard and insulative thine surface treatment layer 13 is applied to an outer circumferential surface of the electrode body 11. This layer 13 forms aluminum oxide or titanium oxide. A workpiece 5 is placed on the elec trode body 11 so as to be covered. An exposed part 11a and the ouflow port 12a are confronted to a machining part of the workpiece 5, namely, a burr 8, making an electrolyte flow therein, and electrolyzation takes place so that the burr 8 dissolved and eliminated. Since there is almost no wear in a electrode, it is usable for a long period of time.