An oxide etching method includes loading an object to be processed, on a surface of which a patterned silicon oxide film is formed, in a chamber, supplying HF gas and NH3 gas as reactant gases and a diluent gas to the chamber to conduct a reaction treatment in which the HF gas and the NH3 gas are reacted with the silicon oxide film. Thereafter, a heating process is performed to remove a reaction product generated by the reaction treatment. In the reaction treatment, a pressure in the chamber is increased to a predetermined value by increasing a flow rate of the diluent gas so that no etching residue remains and an etching shape has high verticality after the heating process.