Epoxy resin is pretreated with an organic solvent such as furfuryl alcohol, methyl alcohol, ethyl alcohol, n-propyl alcohol, iso-propyl alcohol, formic acid, acetic acid, propionic acid, butyric acid, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, acetone, diethyl ketone, dipropyl ketone, methylethyl ketone, diisopropyl ketone, methylpropyl ketone, ethylpropyl ketone, acetonitrile and nitromethane as a pretreating solution, and the pretreated resin is then etched with an etching solution containing hydrogen peroxide or a persulfate and sulfuric acid, or the resin is pretreated with an organic solvent containing furfuryl alcohol, methyl alcohol, ethyl alcohol, n-propyl alcohol or isopropyl alcohol, and formamide or ethylene glycol, 1,2-propylene glycol or glycerine, and the pretreated resin is etched with an etching solution containing hydrogen peroxide and sulfuric acid to roughen the surface of the resin. A good adhesiveness is obtained between the surface of the resin and a film of metal when the resin is coated with a metal.