Abstract: The present invention provides a method for manufacturing a magnetoresistive effect device which can improve the through-put and achieve a high MR ratio. A method for manufacturing a magnetoresistive device according to an embodiment of the present invention includes steps of: forming a first ferromagnetic layer; forming a tunnel barrier layer on the first ferromagnetic layer in a first chamber; and forming a second ferromagnetic layer on the tunnel barrier layer, wherein the step of forming the tunnel barrier layer includes steps of: forming a metal layer on the first ferromagnetic layer; oxidizing the metal layer; and, before the step of forming the second ferromagnetic layer, reducing a pressure inside the first chamber to a predetermined pressure at which the metal layer vaporizes, while keeping a temperature inside the first chamber at a predetermined temperature.