Disclosed herein is a battery pack including a power supply unit including two or more battery cells or battery modules electrically connected to each other, at least one pressure driven switch configured to cause a short circuit in a portion or the entirety of the battery pack upon detecting expansion in volume of the battery cells or the battery modules when the power supply unit malfunctions, a cut-off portion located at at least one series connection region between the battery cells or the battery modules to interrupt electrical connection in the battery pack when the short circuit occurs in the battery pack, and external input and output terminals connected to electrode terminals located at outermost sides of the power supply unit to supply power to an external device.