A method of etching silicon oxide on a surface of a substrate is provided. The method comprises alternately repeating heating the substrate to a heating temperature of 60° C. or higher, supplying hydrogen fluoride gas and ammonia gas onto the substrate to react with the silicon oxide, and modifying the silicon oxide to obtain a reaction product, and removing at least a portion of the reaction product from the substrate while stopping the supply of the above gases and continuing to heat the substrate at the heating temperature; and when a process gas that is at least one of the hydrogen fluoride gas and the ammonia gas is supplied, while continuing to supply the process gas from an upstream side of a flow path, closing a valve disposed in the flow path to pressurize the process gas in the flow path, and then opening the valve.