A Lewis acid-base reaction is caused, in a solution, between a first monomer corresponding to a Lewis acid and a second monomer corresponding to a Lewis base, so as to generate a monomer adduct in which the first monomer and the second monomer are bonded to each other through weak electric interaction. Next, the solution including the monomer adduct is applied on a substrate so as to form a supramolecular solid thin film made of the monomer adduct. Then, the supramolecular solid thin film is heated so as to cause a polymerization reaction between the first monomer and the second monomer within the supramolecular solid thin film, thereby forming a polymer thin film.