PURPOSE: To realize an accurate and fast processing by making a workpiece and a processing electrode to follow a particularly assigned track of motion so that the outline and the shape of all or a part of a circle or an oval may be obtained.

CONSTITUTION: A roughly processed workpiece 1 is installed on a processing table 3 in such a way as to project from it. The table 3 is supported movably in the direction of an axis Y. A processing electrode 2, which has a flat surface 6 facing a workpiece 1 with a discharge processing gap between, is provided with a rotary shaft 7, vertical to XY plane, and makes a rotary motion in response to the rotation of a pulse motor 8. Correspondingly to an angle of rotation θ from an axis X of the processing electrode 2, the workpiece 1 is sent in the derection of the axis Y by a pulse motor 4 and a screw rod 5, while the feed control is maintained to satisfy the condition; l=±(acos2θ+bsin2θ)1/2.r/a.b1/2cosθ. whene "l" means the distance between the center 0 of the workpiece 1 and the rotary shaft 7.