There is provided a micro pattern forming method including forming a thin film on a substrate; forming a film serving as a mask when processing the thin film; processing the film serving as a mask into a pattern including lines having a preset pitch; trimming the pattern including the lines; and forming an oxide film on the pattern including the lines and on the thin film by alternately supplying a source gas and an activated oxygen species. Here, the process of trimming the pattern and the process of forming an oxide film are consecutively performed in a film forming apparatus configured to form the oxide film.