There is provided a technique that includes forming a film in a concave portion provided on a surface of a substrate by performing a cycle a predetermined number of times, the cycle including: (a) supplying a precursor to the substrate; (b) supplying a nitrogen-containing reactant to the substrate; and (c) supplying an oxygen-containing reactant to the substrate, wherein in (c), an oxide layer is formed by oxidizing a layer, which has been formed in the concave portion before (c) is performed, and an amount of oxidation of the oxide layer formed in an upper portion in the concave portion is made larger than an amount of oxidation of the oxide layer formed in a lower portion in the concave portion.