Secondary battery

A secondary battery is provided with: a flexible exterior member (10); a battery element (20) housed inside the exterior member and having a flat shape; first wiring members (30, 40) extending from the inside to the outside of the exterior member; and a plurality of second wiring members (50, 60) disposed inside the exterior member and joined to the first wiring members, the battery element including electrode current collectors (21A, 22A) having a positive electrode active material layer (21B) or a negative electrode active material layer (22B) formed on at least one surface, the electrode current collectors including a plurality of exposed portions (21AH, 22AH) in which the positive electrode active material layer or the negative electrode active material layer is not formed, each of the plurality of exposed portions is provided with a collector joining portion (55) that joins the electrode collector and the plurality of second wiring members, the ratio of the area of the second wiring members to the area o