There is provided a film forming method including: adsorbing fluorine onto a substrate on which a region in which a nitride film is exposed and a region in which an oxide film is exposed are provided adjacent to each other by supplying a fluorine-containing gas to the substrate, and forming a stepped surface on a side surface of the oxide film by selectively etching the nitride film, among the nitride film and the oxide film, so as to cause a surface of the nitride film to be more deeply recessed than a surface of the oxide film; and after the adsorbing the fluorine onto the substrate and forming the stepped surface, selectively forming a semiconductor film on the nitride film, among the nitride film and the oxide film, by supplying a raw material gas including a semiconductor material to the substrate.