To provide a manufacturing method of a spark erosion electrode wire having a diffusion area and a conductive wire core surrounded by a metal cover suited so as to constitute the wear area of a wire during a spark erosion.

A conductive electrode wire is passed through a melted salt bath 3 maintained to the temperature of the melting point or more of a salt. A main power source flows a current between the electrode wire 1 in the melted salt bath and a positive pole and a metal cover layer is piled on the core of the electrode wire 1 electrolytically. The high temperature of the melted salt bath diffuses the core and the metal of the cover mutually and surely. Thereby, the cover structure obtained by the selection of an electrolysis and a diffusion parameter is diversified.