Disclosed is a battery pack, which includes a battery module assembly; a first end plate and a second end plate respectively installed at the battery module assembly; a first pressure adjustment bar fixed to the first end plate; and a second pressure adjustment bar fixed to the second end plate, wherein the first pressure adjustment bar includes an accommodation space formed so that the second pressure adjustment bar is slidably inserted therein; and a plurality of hook holes formed along a sliding direction of the second pressure adjustment bar, wherein the second pressure adjustment bar has an elastic hook elastically coupled to any one of the hook holes selectively so that when the second pressure adjustment bar slides along the accommodation space, the second pressure adjustment bar is released from any one of the hook holes and then coupled to another one of the hook holes. Since the interval between the end plates is automatically adjusted step by step, the pressure between the battery module assembly and the end plates may be automatically maintained consistently.