A secondary battery is provided with a safety vent that can decrease the increased inner pressure of the secondary battery by being rapidly fractured when the inner pressure of the secondary battery is increased over a predetermined value. The secondary battery is constructed with a sealed outer case forming a receiving space in an inner side, an electrode assembly received in the receiving space of the outer case, a safety vent formed on one surface of the outer case, and a fracture induction part formed on the surface of the outer case and disposed at a portion of a circumference region of the safety vent. The fracture induction part is relatively thinner than the other portion of the surface of the outer case.