In a substrate like a printed circuit board comprising an insulator and a copper layer laminated on part of the insulator, said insulator outer surface and said copper layer outer surface are simultaneously subjected to a process (1) comprising treatment with an alkali metal hydroxide solution, a process (2) comprising treatment with an alkaline aqueous solution containing an aliphatic amine, a process (3) comprising treatment with an alkaline aqueous solution having a permanganate concentration of 0.3 to 3.5 wt % and a pH of 8 to 11, a process (4) comprising treatment with an acidic microemulsion aqueous solution containing a thiophene compound and an alkali metal salt of polystyrenesulphonic acid, and a process (5) comprising copper electroplating, which are implemented sequentially.