Discussed herein is a battery pack configured to have a structure in which a battery pack case is provided at the upper part and the lower part thereof with a coolant inlet port and a coolant outlet port, respectively, the battery pack case is provided with a coolant introduction part and a coolant discharge part, the coolant introduction part includes (a) a parallel introduction part adjacent to the coolant inlet port, the parallel introduction part extending in parallel to a top of the unit cell stack and (b) an inclined introduction part connected to the parallel introduction part, the inclined introduction part extending from the coolant inlet port to an end of the battery pack case opposite to the coolant inlet port such that a distance between the inclined introduction part and the top of the unit cell stack is gradually decreased.