SQUARE SECONDARY BATTERY

PROBLEM TO BE SOLVED: To provide a high reliability square secondary battery provided with a current cutoff mechanism between an electrode body and a terminal member, the current cutoff mechanism being resistant to breakage even when a mechanical shock is applied to the battery.SOLUTION: This square secondary battery is provided with a first insulation member 34 having a first through-hole 34a between a first region 16a of a positive electrode collector 16 and a reversal plate 33, the first region 16a of the positive electrode collector 16 and the reversal plate 33 being connected at a position corresponding to the first through-hole 34a. The first insulation member 34 is provided with a fixed part 34f having a first region extending from a body part 34k of the first insulation member 34 to a mouth-sealing body 13 and a second region formed in the first region and protruding from the first region toward a conductive member 32. The fixed part 34f is secured to the conductive member 32, the width at tip in the second region being smaller than the width at root in the second region.