Disclosed are method and apparatus for manufacturing a magnetoresistive device which are suitable for manufacturing a high-quality magnetoresistive device by reducing damages caused during the processing of a multilayer magnetic film as a component of the magnetoresistive device, thereby preventing deterioration of magnetic characteristics due to such damages. Specifically disclosed is a method for manufacturing a magnetoresistive device, which includes processing a multilayer magnetic film by performing a reactive ion etching on a substrate which is provided with the multilayer magnetic film as a component of the magnetoresistive device. This method for manufacturing a magnetoresistive device includes irradiating the multilayer magnetic film with an ion beam after the reactive ion etching.