A method of rapidly forming a thin film of high quality through film formation by alternate feeding of raw gases. In particular, a method of forming a TiN thin film, comprising repeating operations including causing TiCl4 gas as a raw gas to be adsorbed on a substrate or TiCl4 molecules adsorbed on a substrate and feeding NH3 gas as a reactant gas in a treating chamber so as to effect reaction ofTiCl4 and NH3 leading to formation of a TiN film, which method further comprises an operation of, prior to the adsorption of TiCl4 gas on the substrate, feeding reducing H2 gas in the treating chamber(30) so as to change TiCl4 to a state of enhanced likelihood of adsorption on the substrate (e.g., TiCl3).