Constructing a battery pack by: providing a resin sheet (40) to cover a release opening (20a) of a safety vent (20) formed on a sealing plate (23); integrating a rechargeable battery (2) and a circuit substrate (3) with a primary molding (11) by filing a resin between the rechargeable battery (2) and the circuit substrate (3); and then forming a secondary molding (12). In such constructed battery pack, an ejected gas, at the operation of the safety vent (20) of the battery pack, is externally released through an interface between the resin and metal.