Provided is a substrate processing method, which can fill an insulating film in a groove having a small width with a high aspect ratio and improve the productivity. The substrate processing method comprises loading a substrate into a processing chamber, supplying silicon compound gas including carbon and hydrogen into the processing chamber, irradiating ultraviolet light on the silicon compound gas supplied into the processing chamber to process the substrate, unloading the processed substrate from the processing chamber, and processing the inside of the processing chamber with excited oxygen-containing gas. Accordingly, an adhered matter generated when irradiating the ultraviolet light on the silicon compound gas to process the substrate and adhered to a structure such as an inner wall of the processing chamber can be processed with the excited oxygen-containing gas to modify it.