A method for producing an IC card including filling a confined space with a mixture including a foaming resin, the mixture having not been foamed yet, the space being confined by a frame having cut-out portions on inner edges and at least one through-hole passing through the frame in the lateral direction between the inside and the outside of the frame, a circuit board on which functional components are mounted and having edges fitted to one of the cut-out portions of the frame so that the surface of the circuit board on which functional components are mounted faces inward, the frame and the circuit board forming a substantially flat outer surface, and a thin plate having edges fitted to another of the cut-out portions of the frame with the thin plate opposing the circuit board, the frame and the thin plate forming a substantially flat outer surface; foaming the mixture at a predetermined temperature for a predetermined time, thus filling the confined space with foamed resin, and thus making the foamed resin a structural member having mechanical strength, molding the frame, the circuit board, and the thin plate into one body; and removing excess foamed resin from the through-hole in the frame.