A button-type secondary battery, in which an electrode assembly is mounted in a lower can , and an upper can is coupled to the lower can , wherein the button-type secondary battery has a first end in a height direction, which is an upper end, and a second end in the height direction, which is a lower end, the button-type secondary battery comprising: the lower can having a first sidewall in a vertical direction along a circumference of a first flat portion ; an upper can having a second sidewall in a vertical direction along a circumference of a second flat portion , wherein the upper can is coupled to the lower can so that the second flat portion faces the first flat portion , and the second sidewall is disposed outside the first sidewall ; an electrode assembly in which a negative electrode, a separator, and a positive electrode are wound in a state of being stacked and which is mounted in an inner space between the lower can and the upper can so that the negative electrode is connected to the lower can , and the positive electrode is connected to the upper can ; and a gasket disposed between the second sidewall and the first sidewall to prevent the upper can and the lower can from being in contact with each other, wherein the second sidewall comprises a distal end that is bent to surround an edge configured to connect the first flat portion to the first sidewall and is disposed below the first flat portion , and the gasket extends to be disposed between the distal end and the first flat portion , wherein an exposed portion protruding to the outside through the distal end is formed on an end of the gasket , and the exposed portion is disposed below the first flat portion , and the exposed portion is expanded downward from the distal end and is bent to cover a portion of a bottom surface of the distal end . the lower can having a first sidewall in a vertical direction along a circumference of a first flat portion ; an upper can having a second sidewall in a vertical direction along a circumference of a second flat portion , wherein the upper can is coupled to the lower can so that the second flat portion faces the first flat portion , and the second sidewall is disposed outside the first sidewall ; an electrode assembly in which a negative electrode, a separator, and a positive electrode are wound in a state of being stacked and which is mounted in an inner space between the lower can and the upper can so that the negative electrode is connected to the lower can , and the positive electrode is connected to the upper can ; and a gasket disposed between the second sidewall and the first sidewall to prevent the upper can and the lower can from being in contact with each other, wherein the second sidewall comprises a distal end that is bent to surround an edge configured to connect the first flat portion to the first sidewall and is disposed below the first flat portion , and the gasket extends to be disposed between the distal end and the first flat portion , wherein an exposed portion protruding to the outside through the distal end is formed on an end of the gasket , and the exposed portion is disposed below the first flat portion , and the exposed portion is expanded downward from the distal end and is bent to cover a portion of a bottom surface of the distal end . <EOS>