A pattern-forming method for forming a predetermined pattern serving as a mask when etching film on a substrate includes the steps of: an organic film pattern-forming step for forming an organic film pattern on a film to be processed; forming a silicon nitride film on the organic film pattern; etching the silicon nitride film so that the silicon nitride film remains only on the lateral wall sections of the organic film pattern; and removing the organic film, thereby forming the predetermined silicon nitride film pattern on the film to be processed on a substrate. With the temperature of the substrate maintained at no more than 100° C., the film-forming step excites a processings gas and generates a plasma, performs plasma processing with the plasma, and forms a silicon nitride film having stress of no more than 100 MPa.