The invention provides a high-reliability prismatic secondary battery, including a current interruption mechanism between a collector and an external terminal, the current interruption mechanism which is unlikely to be damaged even if the battery is subjected to shock due to vibration, falling, etc. The current interruption mechanism for prismatic secondary battery includes a tubular portion (32a) of a conductive member (32) electrically connected to a positive electrode external terminal (17), an inversion plate (33) sealing one end of the tubular portion, and a positive electrode collector (16) connected to the inversion plate. The positive electrode collector has a first region (16a) that is parallel to a sealing body (13) and a second region (16b) that extends from the first region in the direction of the electrode assembly and is connected to the positive electrode plate. The boundaries (16f) 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.