The secondary battery comprises: a battery element 20 having a positive electrode 30 wherein positive active material 31 are applied on both surfaces of a positive current collector 32, a negative electrode 40 wherein negative active material 41 are applied on both surfaces of a negative current collector 42, and a separator; a packaging film 10, made of a film that includes a heat-seal resin layer 13, for accommodating the battery element; wherein a melting point or a decomposition temperature of the separator is higher than a melting point of the heat-seal resin layer by 50° C. or more; and wherein, at least a part of the active material layer 31, 41 of the positive electrode or the negative electrode and the heat-seal resin layer are heat-sealed to each other at at least one surface of the upper surface and the lower surface of the battery element.