A battery pack includes a battery unit including rectangular secondary batteries, each including a sealing plate and positive and negative electrode terminals attached to the sealing plate; a bus bar that connects the rectangular secondary batteries together in parallel; an insulating plate disposed between the sealing plates of the rectangular secondary batteries and the bus bar; and a short-circuit breaking portion that interrupts an electric conduction path between the rectangular secondary batteries connected in parallel by allowing each sealing plate to bulge outward in response to an internal pressure rise of the battery to push up the insulating plate and the bus bar. A portion of each sealing plate that bulges most protrudes outward by greater than or equal to 1.5 mm from an outer peripheral edge of the sealing plate when a pressure in the corresponding rectangular secondary battery reaches the operating pressure of a gas release valve.