Disclosed herein is a cap assembly loaded on an open upper end of a metal battery can of a cylindrical secondary battery. The cap assembly includes a top cap located at the uppermost end of the cap assembly, a safety vent located under the top cap and electrically connected to the top cap via a safety vent for discharging gas, a current interrupt device configured such that a portion of the upper surface of the current interrupt device is connected to the safety vent and a portion of the lower surface of the current interrupt device is connected to an electrode lead of an electrode assembly, and a current interrupt device (CID) gasket coupled to the current interrupt device so as to wrap an outer circumferential part of the current interrupt device in order to secure the electrical insulation property of the current interrupt device.