A square secondary battery of an embodiment includes an outer can formed in a shape of a bottomed cylinder having a cross-sectional shape of a substantially quadrangular shape, the outer can having an opening, a power generation element contained in the outer can, and a lid having a positive electrode terminal and a negative electrode terminal, the lid covering the opening of the outer can. Two or more convex portions exist on each of one or more surfaces of a side surface of an outer surface of the outer can, a bottom surface of the outer surface of the outer can, and a surface having the positive electrode terminal and the negative electrode terminal of an outer surface of the lid.