A resin board that consists of at least one of a mixture of a plurality of types of resins having different degrees of susceptibility to erosion by an ozone solution, and a resin having, in a molecule, a plurality of types of components having different degrees of susceptibility to erosion by the ozone solution is treated with ozone water to form a reformed layer, and a catalyst metal is adsorbedby the reformed layer so as to form a resin-metal composite layer, on which a plating process is performed. In the resin board, a component or components that is/are likely to be eroded on by the ozone solution dissolves into the ozone solution, and pores or clearances on the order of nanometers are formed between the component(s) and a component or components that is/are less likely to be erodedby the ozone solution. With the plating deposited in the pores or clearances, the adhesion strength is improved due to an anchoring effect. Thus, the adhesion strength of the plating film is improvedeven where the resin-metal composite layer has a thickness of 10 to 200nm.