Provided is an apparatus for forming a silicon-containing thin film, the apparatus including a controller which is configured to control a process gas supplying mechanism, a heating device, and an exhauster to perform: forming a first seed layer on a base by adsorbing at least silicon included in an aminosilane-based gas on the base, using the aminosilane-based gas; forming a second seed layer on the first seed layer by depositing at least silicon included in a higher-order silane-based gas having an order that is equal to or higher than disilane, using the higher-order silane-based gas having an order that is equal to or higher than the disilane, wherein the first seed layer and the second seed layer form a dual seed layer; and forming the silicon-containing thin film on the dual seed layer.