The present invention provides a cap assembly of a cylindrical secondary battery, comprising a top cap, a PTC element, and an integrated gasket in which a first gasket covering a safety vent and a second gasket covering a current cut-off member are integrated. The secondary battery comprising the thus-configured cap assembly is advantageous in that conventional dual gasket structures are integrated into a unitary gasket structure to increase contact area between the safety vent and the gasket and thus increase sealing effects. Further, the secondary battery of the present invention is advantageous in that the gasket structure freely varies in accordance with the diameter of the current cut-off member, to thereby increase a short-circuit reaction of the current cut-off member, improve safety, and reduce the number of parts and manufacturing costs.