PURPOSE: To generalize a single wire guide for a wire electrode having different diameters and to dispense with inclination of a wire guide head by a method wherein the wire guide of a wire electrode is constituted in combination of an open guide and a closed guide.

CONSTITUTION: A wire electrode 1 is rewound from a reel and fed in a Z- direction through a machining device. A current source 2 to supply a pulse from an electrical machining source extrude the wire electrode 1 from a vertical direction. In which case, a wire guide 3 is arranged and a closed guide 4 consisting of an annulus ring is arranged downstream of an open guide 3 and a closed guide 4 consisting of an annulus ring is arranged downstream of the open guide 3. In this case, the open guide 3 guides a wire electrode 1 in a case of conical cut being executed, slide of the wire electrode 1 is prevented at acute angles A and B. Meanwhile, at further acute angles C and D, the closed guide 4 guides the wire electrode 1. This constitution generalizes single wire guides 3 and 4 for a wire electrode 1 having different diameters.