Abstract: A protective circuit having an electronic circuit constructed on a circuit board is built into a sealing member that seals the open end of a battery case accommodating electricity generating elements. The circuit board is attached to the outer end of the sealing member. A positive terminal plate that becomes the positive terminal of the secondary battery and an S pole terminal plate that controls the operation of the electronic circuit by an external connection are provided on the outer surface of the circuit board. Thereby, a protective circuit that prevents over-discharging and overcharging is arranged inside the sealing member. A secondary battery is thereby constructed with a protective circuit without resorting to a construction of a battery pack.