An energy storage device may include an electrode assembly including electrodes and separators, wherein the electrodes and separators are alternately stacked in a vertical direction of the energy storage device; an external member accommodating the electrode assembly therein; and electrode leads joined to the electrodes provided in the electrode assembly, the electrode leads are provided in the external member, the electrodes include a positive electrode and a negative electrode, the electrode leads include: a positive electrode lead having one side joined to the positive electrode; and a negative electrode lead having one side joined to the negative electrode, first and second through holes are provided in upper and lower surfaces of the external member, respectively, in the vertical direction, and a portion of the positive electrode lead is provided to face the first through hole in the external member, and a portion of the negative electrode lead is provided to face the second through hole in the external member.