An object of the present invention is to provide a method for forming a recess portion having an predetermined shape on one side of a metal plate without giving the metal plate any remarkable stress while forming the other side flat, which is suitable for a package for electronic parts such as an integrated circuit, etc. The method according to the present invention is characterized in that a recess portion having an predetermined shape is formed by plastically deforming a metal plate having a predetermined thickness by means of a press, etc. so as to form the recess portion having a depth smaller than the thickness on one side thereof and to form at the same time a protruding portion protruding on the other side of the metal plate. In the steps of plastically deforming the metal plate, metal corresponding to the recess portion is displaced to the protruding portion. Then, the protruding portion on the other side is removed by cutting processing to form the recess portion only on the one side of the metal plate and to form the other side flat.