A prismatic secondary battery includes a prismatic hollow outer body having a mouth and a bottom; a flat electrode assembly, a positive electrode collector, a negative electrode collector, and an electrolyte, all of which are stored in the prismatic outer body; a sealing plate sealing up the mouth of the prismatic outer body; and a positive electrode terminal attached to the sealing plate in an electrically insulated manner. The sealing plate includes a gas release valve and an electrolyte pour hole and further includes, on the front face, a concaved flat face having an identification code. With the prismatic secondary battery of the invention, a jig for assembly or the like is unlikely to come into contact with the identification code during an assembly process of the prismatic secondary battery, hence the identification code is unlikely to be abraded, and the traceability is unlikely to be lost.