A rectangular secondary battery (1) includes a current interrupting portion (60) disposed in a current path between a collector plate (21) connected to a rolled electrode group (40) and an external terminal (61) and configured to interrupt the current path when an internal pressure of a battery container (2) is increased. The current interrupting portion (60) has a diaphragm (68) whose top portion (68a) is electrically connected to the collector plate (21) and whose edge portion (68b) is electrically connected to the external terminal (61). The diaphragm (68) is formed into a convex shape protruding inside the battery container (2) and into a planar shape elongated in a longitudinal direction of the battery container (2).