After forming a conductive layer on the entire surface of an insulation substrate, a resin mask of poly lactic acid etc. resin which will hydrolyze in an alkali aqueous solution is integrally formed on the insulation substrate so that a part to which a conductive layer of a predetermined pattern is to be formed is exposed. Then, a conductive layer is overlaid on the part exposed from the resin mask by means of electrolytic plating using an acidic bath composition. The interface between the resin mask of poly lactic acid etc. resin and the conductive layer reproduces an accurate contour of the pattern. Thereafter, the resin mask is efficiently removed by hydrolysis using an alkali aqueous solution, and finally the conductive layer is removed by chemical etching to thereby form a conductive layer having the predetermined pattern on the surface of the insulation substrate.