Disclosed herein is a battery pack including a battery cell, having an electrode assembly mounted in a pouch-shaped battery case made of a laminate sheet including a metal layer and a resin layer and is sealed by thermal welding, mounted in a pack case, wherein the pack case includes a frame member constructed in a structure in which a receiving part for receiving the battery cell is open, opposite side sealing portions of the battery cell are mounted to the frame member such that the opposite side sealing portions cover the opposite sides of the frame member, and a sheathing film is applied to the outer surface of the frame member, to which the battery cell is mounted.