Disclosed herein is a cap assembly loaded on an open upper end of a cylindrical container of a battery in which an electrode assembly is mounted in the cylindrical container, the cap assembly including a safety vent having a predetermined notch configured to rupture by high-pressure gas generated in the battery, a current interruptive device coupled to a bottom of the safety vent by welding for interrupting current when internal pressure of the battery increases, and a current interruptive device gasket for surrounding an outer circumference of the current interruptive device, wherein the current interruptive device includes two or more through holes for gas discharge, the through holes being formed such that the sum of areas of the through holes is equal to 20% to 50% of an entire area of the current interruptive device. When high-pressure gas is generated in the battery, the cap assembly effectively interrupts current and rapidly discharges the gas, thereby greatly improving safety of the battery.