A solution containing a metal component of composite ultrafine metal particles each having a core substantially made of metal component and a covering layer made of an organic compound chemically bonded to the core having an average diameter ranging from 1 to 10 nm, uniformly dispersed in a solvent, forms a thin metal film on the surface of a transfer sheet, after which the transfer sheet, after which the transfer sheet is thermally decomposed to transfer the thin metal film to a substrate.