A battery pack has a case. The case has battery cells received therein. The case has a closed-bottom cylindrical case body and a flat plate-shaped lid body. Each of the walls of the case body has an end surface surrounding the opening of the case body. A seal member is provided to the end surfaces of the walls. The seal member has an inner overlapping portion and an outer overlapping portion, which overlap each other. Because of the presence of a sixth bend, the inner overlapping portion has restoring force acting toward the outer overlapping portion.