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 comprising: a safety vent having a predetermined notch configured to rupture by high-pressure gas generated in the battery for discharge of the high-pressure gas in a straight line; 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 comprises 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, wherein a center of the safety vent is provided with a depression configured to be depressed downward, an upper bent portion and a lower bent portion of the safety vent forming the depression are provided with a first notch and second notches, respectively, and the first notch, formed at the upper bent portion of the safety vent, is configured in a shape of an open curve, one side of which is open, and wherein the first notch has a greater depth than the second notches such that the first notch is configured to rupture before the second notches, wherein a center of the current interruptive device gasket is provided with an opening, and the central opening is configured in a shape not to cover the through holes of the current interruptive device, and wherein the through holes of the current interruptive device, the opening of the current interruptive device gasket, and a notch of the safety vent are aligned with one another in a straight line such that the through holes of the current interruptive device, the opening of the current interruptive device gasket, and the notch of the safety vent communicate with one another. a safety vent having a predetermined notch configured to rupture by high-pressure gas generated in the battery for discharge of the high-pressure gas in a straight line; 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 comprises 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, wherein a center of the safety vent is provided with a depression configured to be depressed downward, an upper bent portion and a lower bent portion of the safety vent forming the depression are provided with a first notch and second notches, respectively, and the first notch, formed at the upper bent portion of the safety vent, is configured in a shape of an open curve, one side of which is open, and wherein the first notch has a greater depth than the second notches such that the first notch is configured to rupture before the second notches, wherein a center of the current interruptive device gasket is provided with an opening, and the central opening is configured in a shape not to cover the through holes of the current interruptive device, and wherein the through holes of the current interruptive device, the opening of the current interruptive device gasket, and a notch of the safety vent are aligned with one another in a straight line such that the through holes of the current interruptive device, the opening of the current interruptive device gasket, and the notch of the safety vent communicate with one another.