A battery pack case adapted to enclose a protective circuit module and a bare cell includes at least one small opening arranged on a side to expose an external terminal of the protective circuit module and a large opening arranged in the opposite direction to the small opening to expose a surface of the bare cell. Since a bare cell and a protective circuit module are contained within an integral case, the bare cell is prevented from escaping out of the protective circuit module and no separate resin is necessary to fill the gap between the bare cell and the protective circuit module. In addition, the battery pack case has gates, through which a resin is injected, which are properly arrayed in such a manner during resin injection that the case has no unshaped part.