Disclosed herein is a battery pack case in which a battery module having a plurality of stacked battery cells or unit modules (‘unit cells’) is mounted, wherein the 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, which are directed in opposite directions such that a coolant to cool the unit cells can flow from one side to the other side of the battery module in a direction perpendicular to a cell stacking direction, the battery pack case is further provided with a flow space (‘coolant introduction part’) extending from the coolant inlet port to the battery module and another flow space (‘coolant discharge part’) extending from the battery module to the coolant outlet port, and the flow channel width of the coolant introduction part and/or the flow channel width of the coolant discharge part is greater than that of each of the unit cells, thereby achieving uniform distribution of the coolant.