Provided is a secondary cell in which a single-layer secondary cell has an all-solid-state secondary cell structure comprising a storage layer sandwiched by a positive electrode layer and a negative electrode layer, and which is superior to conventional secondary cells with respect to capacity, operation and/or positioning. This secondary cell is characterized by the use of a folded single-layer secondary cell formed by folding a sheet-shaped single-layer secondary cell, which comprises a storage layer sandwiched between a positive electrode layer and a negative electrode layer, two or more times while alternately reversing the folding direction.