A secondary battery including an electrode assembly, the electrode assembly including a first electrode, a second electrode, and a separator; a case accommodating the electrode assembly therein; a cell cover sealing the case; and a first terminal unit having one end that is electrically connected to the first electrode of the electrode assembly and having another end extracted to an outside of the case, wherein the first terminal unit includes a first collector in the case and electrically connected to the first electrode of the electrode assembly, the first collector having a fuse area; and an arc cutting block adjacent to the fuse area of the first collector, the arc cutting block being movable to a position previously occupied by the fuse area in the event that the fuse area is cut off, and cutting an arc generation path.