A rechargeable battery according to an embodiment of the present invention includes: a first case receiving an electrode assembly and having a first opening; a second case having a second opening smaller than the first opening and coupled to the inner surface of the first case with the outer surface while covering the electrode assembly; an insulating material interposed between the first case and the second case to form an electrically insulating state; a plurality of protruded parts protruded onto the outer surface of the second case; and a plurality of accommodating parts formed in the first case and coupled to the protruded part, wherein the first case and the second case are concluded to form a closed state when the protruded part is coupled to the accommodating part.