A cap assembly comprising: a base plate mounted to an open upper end of a battery case; a protection circuit module mounted on the base plate; and a top cap coupled to the upper end of the battery case while the top cap covers the PCM, the top cap being made of an insulative material, wherein the electrical connection and the mechanical coupling between the PCM and the base plate are accomplished by one forced-inserting type rivet, the PCM has two through-holes (a, b) connected to a cathode and an anode of a battery, respectively, and the base plate is provided with a coupling member and a through-hole (c) corresponding to the through-holes of the PCM, respectively, while the PCM is positioned on the base plate, the coupling member is inserted through the through-hole (a), the rivet is inserted through the through-hole (b) and through-hole (c) so as to accomplish the electrical connection and mechanical coupling between the PCM and the base plate, and a gasket mounted at the through-hole (c) of the base plate, through which the rivet is inserted, such that the gasket covers the upper end surface, the lower end surface, and the inner circumferential surface of the through-hole (c), the gasket being made of an insulative material, wherein the rivet includes a cylindrical body and a plate-shaped body, having a predetermined thickness, formed at the middle of the cylindrical body, such that the rivet serves to space the PCM and the base plate by a predetermined distance from each other, and the rivet constitutes a protruding terminal located on the base plate, and wherein the base plate is provided around the through-hole (c) thereof, through which the rivet is inserted, with a depression, in which the plate-shaped body of the rivet is located. a base plate mounted to an open upper end of a battery case; a protection circuit module mounted on the base plate; and a top cap coupled to the upper end of the battery case while the top cap covers the PCM, the top cap being made of an insulative material, wherein the electrical connection and the mechanical coupling between the PCM and the base plate are accomplished by one forced-inserting type rivet, the PCM has two through-holes (a, b) connected to a cathode and an anode of a battery, respectively, and the base plate is provided with a coupling member and a through-hole (c) corresponding to the through-holes of the PCM, respectively, while the PCM is positioned on the base plate, the coupling member is inserted through the through-hole (a), the rivet is inserted through the through-hole (b) and through-hole (c) so as to accomplish the electrical connection and mechanical coupling between the PCM and the base plate, and a gasket mounted at the through-hole (c) of the base plate, through which the rivet is inserted, such that the gasket covers the upper end surface, the lower end surface, and the inner circumferential surface of the through-hole (c), the gasket being made of an insulative material, wherein the rivet includes a cylindrical body and a plate-shaped body, having a predetermined thickness, formed at the middle of the cylindrical body, such that the rivet serves to space the PCM and the base plate by a predetermined distance from each other, and the rivet constitutes a protruding terminal located on the base plate, and wherein the base plate is provided around the through-hole (c) thereof, through which the rivet is inserted, with a depression, in which the plate-shaped body of the rivet is located.