A method for producing an epitaxial silicon wafer by applying a vapor deposition on a silicon wafer is disclosed. A vapor deposition apparatus in which the vapor deposition is conducted at least includes a chamber and a hydrogen-chloride-gas supply apparatus that is in communication and connected with an inside of the chamber to supply hydrogen chloride gas into the chamber. A valve including a diaphragm that allows or blocks a flow of the hydrogen chloride gas from an inlet channel to an outlet channel is disposed in the hydrogen-chloride-gas supply apparatus. A W-free anticorrosion alloy material is used for the diaphragm. When a maintenance work is to be done inside the chamber, the hydrogen chloride gas is supplied from the hydrogen-chloride-gas supply apparatus into the chamber.