Disclosed herein is a battery pack case configured to receive a battery module assembly including a plurality of battery modules, each having a plurality of battery cells or unit modules mounted therein, sequentially stacked, wherein a coolant inlet port and a coolant outlet port are located at the upper part and the lower part of the battery pack case, respectively, in a state in which the coolant inlet port and the coolant outlet port are opposite to each other such that a coolant for cooling the unit modules flows from one side of the battery modules to the opposite side of the battery modules in a direction perpendicular to a direction in which the unit modules are stacked, and an inclined plate for guiding the flow of the coolant is provided between the battery pack case and the battery modules.