PURPOSE: To improve strength at high temperature and a machining rate by forming a copper-zinc alloy layer of predetermined thickness on the external surface of a copper coated steel wire with a coverage rate of 10W70% in such a way that zinc concentration becomes higher toward an external layer.

CONSTITUTION: A copper coated steel wire 11 with a coverage rate of 10W70% is used as a core material and a copper-zinc alloy layer 12 of approximately uniform thickness within a range of 1W15μm is formed on the external surface of the wire 11, thereby forming a wire electrode of about 0.2mm overall diameter. Said copper-zinc alloy layer 12 has 3-layer structure, comprising an uppermost layer 13 of 55W65% zinc concentration, an intermediate layer 14 of 40W48% zinc concentration and an inner layer 15 of 40% or less zinc concentration. According to the aforesaid constitution, strength at high temperature is improved with high conductivity maintained and a copper deposit on a workpiece due to an exposed copper layer is prevented, thereby enabling the improvement of a machining rate.