Disclosed herein is a battery pack including two or more plate-shaped battery cells arranged in plane such that electrode terminals of the battery cells are aligned in one direction, a pack frame including two or more battery cell receiving parts surrounding outer circumferences of the battery cells in a state in which upper and lower surfaces of the battery cells arranged in plane are opened, a pack frame including a receiving part to receive the two or more plate-shaped battery cells, the receiving part surrounding outer circumferences of the battery cells in a state in which upper and lower surfaces of the battery cells arranged in plane are opened, a protection circuit module (PCM) electrically connected to the electrode terminals to control operation of the battery pack, a middle mold to receive the PCM, the middle mold being loaded on the sealed surplus portions, an electrically insulative member applied into a space defined by the sealed surplus portions and the pack frame and onto the middle mold and the PCM, and a label to cover the battery cells, the pack frame, and the electrically insulative member.