The present invention relates to a cap assembly and a circular secondary battery comprising same and particularly to a cap assembly for a circular battery, which is mounted on the upper end of the circular secondary battery having a structure wherein an electrode assembly is embedded in a circular can, and to a circular secondary battery comprising same, the cap assembly comprising: a safety belthaving predetermined notches so as to be burst by the high-pressure gas of the battery; a current breaking member, which is coupled to the lower end of the safety belt and breaks an electric current in case of an increase in the internal pressure of the battery; and a gasket for the current breaking member, which surrounds the outer circumferential surface of the current breaking member, wherein the gasket for the current breaking member is formed from a polymer resin or a composite of the polymer resin and a ceramic, the polymer resin having a melting point of at least 250 DEG C and a heat deflection temperature of at least 200 DEG C.