A battery pack includes a pack case configured to accommodate a cell module assembly in an inner space thereof and having an opening formed at one side, and a pack cover having a degassing port communicating with the inner space and configured to cover the opening of the pack case. The cell module assembly includes a cell fixing frame having an upper plate and a lower plate respectively disposed at an upper portion and a lower portion of the cell stack and in surface contact with an upper wall and a lower wall of the pack case. At least one of the upper plate and the lower plate includes at least one gas moving route formed by concavely depressing one surface in contact with the upper wall or the lower wall of the pack case along a path toward the degassing port, and at least one hole.