The present invention relates to a secondary battery enabling the enhancement of safety by rapidly releasing gas generated therein. One embodiment discloses a secondary battery comprising: an electrode assembly; a case for receiving the electrode assembly; and a cap assembly coupled to the upper portion of the case and provided with a cap-up, a safety vent installed on the lower portion of the cap-up and having a notch formed therein, and a cap-down coupled to the lower portion of the safety vent, wherein the cap-down comprises a welded part welded to the safety vent from the lower portion of the cap-down.