A current interruption mechanism for prismatic secondary battery includes a tubular conductive member electrically connected to a positive electrode external terminal, an inversion plate, and a positive electrode collector connected to the inversion plate. The positive electrode collector has a first region that is parallel to a sealing body and a second region that is connected to a positive electrode plate. The boundaries between the first and second regions are disposed further outward than the inner surface of the tubular conductive member, and at least one of the edge portions, other than the boundaries between the first region and second region, is located further outward than the inner surface of the tubular portion of the conductive member. The current interruption mechanism is unlikely to be damaged even if the battery is subjected to shock due to vibration, falling, etc.