An insulating film having features such as a low dielectric constant, a low etching rate and a high insulating property is formed. An oxycarbonitride film having a predetermined thickness is formed on a substrate in a process vessel by performing a cycle a predetermined number of times, wherein the cycle includes steps of: (a) performing a set of steps a predetermined number of times to form a carbonitride layer having a predetermined thickness on the substrate; and (b) supplying an oxygen-containing gas into the process vessel to oxidize the carbonitride layer having the predetermined thickness, thereby forming an oxycarbonitride layer, wherein the set of steps includes: (a-1) supplying a gas containing an element into the process vessel accommodating the substrate under a condition where a CVD reaction is caused to form a layer containing the element on the substrate; (a-2) supplying a carbon-containing gas into the process vessel to form a carbon-containing layer on the layer containing the element, thereby forming a layer including the element and a carbon; and (a-3) supplying a nitrogen-containing gas into the process vessel to nitride the layer including the element and the carbon, thereby forming the carbonitride layer.