A highly reliable prismatic secondary battery with a current interruption mechanism that is unlikely to be damaged even if the battery is subjected to shock due to vibration, falling, etc. A second insulating member that has a through-hole is disposed between an inversion plate and the first region of a positive electrode collector, and through the through-hole the first region of the positive electrode collector is electrically connected to the inversion plat. First to third projections to formed around the through-hole formed in the second insulating member fit respectively into first to third openings formed in the first region of the positive electrode collector, and the diameters of their apexes are widened, thus forming first to third fixing portions. Thereby, the second insulating member is robustly joined to the first region of the positive electrode collector.