The method for forming a stopper includes injection molding a stopper molding comprising a molding body portion which embeds an end portion of an element row, and a thin fin portion which extends outward from a periphery portion of the molding body portion on at least one end portion side of the element row, and forming a high frequency wave adhesion portion by adhering the fin portion of the stopper molding by a high frequency wave. By this, a fixing strength of the stopper can be increased, and the high frequency wave adhesion portion can be configured to bend easily by making a thickness of the high frequency wave adhesion portion thin, thereby stably forming the stopper which is difficult to detach for a long period of time.