A battery pack configured to have a structure comprising a plate-shaped battery cell having electrode terminals formed at one side thereof comprising a sealed surplus part and a protection circuit module (PCM) mounted at the sealed surplus part , wherein each of the electrode terminals of the battery cell is made of a plate-shaped conductive member, the PCM comprises a protection circuit board (PCB) , a safety element electrically connected between one of the electrode terminals formed at one side of the battery cell and the PCB or loaded on the PCB , an external input and output terminal electrically connected to a protection circuit of the PCB , and an electrically insulative module case in which the PCB and the safety element are mounted in a state in which the external input and output terminal extends outside, the module case is configured to have a structure in which two outer surfaces of the module case are open outward to form a first open surface and a second open surface , the module case is provided at an interior thereof with a PCB receiving part, and the PCM is loaded on the sealed surplus part of the battery cell in a state in which the PCM is received in the module case such that the PCM is electrically connected to the electrode terminals of the battery cell , characterized in that the plate-shaped battery cell is a pouch-shaped secondary battery having an electrode assembly received in a battery case made of a laminate sheet comprising a resin layer and a metal layer in a sealed state, and the module case is configured to have a tunnel structure in which the first open surface and the second open surface communicate with each other in a straight line, and the first open surface or the second open surface is oriented toward the electrode assembly of the battery cell in a state in which the module case is loaded on the sealed surplus part of the battery cell . each of the electrode terminals of the battery cell is made of a plate-shaped conductive member, the PCM comprises a protection circuit board (PCB) , a safety element electrically connected between one of the electrode terminals formed at one side of the battery cell and the PCB or loaded on the PCB , an external input and output terminal electrically connected to a protection circuit of the PCB , and an electrically insulative module case in which the PCB and the safety element are mounted in a state in which the external input and output terminal extends outside, the module case is configured to have a structure in which two outer surfaces of the module case are open outward to form a first open surface and a second open surface , the module case is provided at an interior thereof with a PCB receiving part, and the PCM is loaded on the sealed surplus part of the battery cell in a state in which the PCM is received in the module case such that the PCM is electrically connected to the electrode terminals of the battery cell , characterized in that the plate-shaped battery cell is a pouch-shaped secondary battery having an electrode assembly received in a battery case made of a laminate sheet comprising a resin layer and a metal layer in a sealed state, and the module case is configured to have a tunnel structure in which the first open surface and the second open surface communicate with each other in a straight line, and the first open surface or the second open surface is oriented toward the electrode assembly of the battery cell in a state in which the module case is loaded on the sealed surplus part of the battery cell . <EOS>