A silica-based interlayer insulating layer having a low dielectric constant is formed with SOG material on a substrate, in which a wiring-layer forming space is then formed. If necessary, a UV ray irradiation is performed under an oxidizing atmosphere. A Si—OH bond is formed on a surface of the insulating layer. A monomolecular layer film is then adhered to the inner surface of the space, which is then modified to be a catalyst with a solution containing Pd compound. On the catalyst monomolecular layer, a copper-diffusion-resistant film is formed by electroless plating, on which a copper plate is then formed as a wiring layer.