A battery pack, which can secure the strength of an outer case, minimize the thickness over the whole outer case and ensure a battery capacity of the battery pack, by forming a portion of a main wall of the outer case with a metal plate. The battery pack includes a core pack, a first case, and a second case. The first case has a periphery including a first resin molding part, and is configured tocover a first surface of the core pack. The second case has a periphery including a second molding part, and is configured to cover a second surface of the core pack. The first and second cases are connected with each other by a weld of the first and second molding parts.