A battery module includes a plurality of flat or square type batteries that each have a positive terminal and a negative terminal; a holder that has an opening, and retains the batteries in such a manner that the positive terminal and the negative terminal are positioned toward the opening, and that the principal surfaces of the batteries face each other; a cover that is disposed over the opening; a circuit board that is disposed over the cover; and a plurality of connection members that are disposed between the cover and the circuit board to electrically connect the positive terminal and negative terminal. Some of the connection members retain a peripheral portion of the circuit board.