Examples of a film forming method includes repeating first processing and second processing in this order a plurality of times, wherein the first processing supplies material-1 having one silicon atom per molecule onto a substrate, and then generates plasma while reactant gas is introduced, thereby forming a silicon oxide film on the substrate, and the second processing provides material-2 having two or more silicon atoms per molecule onto the substrate, and then generates plasma while no reactant gas is introduced, thereby forming a double silicon compound on the substrate.