A substrate processing apparatus includes a processing container; a stage on which a substrate is placed, the stage being provided in the processing container; a gas supply provided at a position facing the stage and configured to supply a first processing gas containing a first monomer and a second processing gas containing a second monomer into the processing container to form a film of a polymer on the substrate; and a driver configured to move the stage so as to change a distance between the gas supply and the stage. The gas supply is configured to supply the first processing gas and the second processing gas into a space between the gas supply and the stage from an outside of a region on the stage in which the substrate is placed, when viewed in a direction from the gas supply toward the stage.