A battery pack includes a battery cell stack formed by a plurality of stacked battery cells, a battery module housing configured to wrap the other outer surfaces of the battery cell stack excluding a first surface and a second surface, from which electrode leads protrude, a water tank configured to supply a coolant to the battery cell or the battery module housing, and a battery pack case configured to receive a plurality of battery module housings. The battery pack case includes a pack case space portion located adjacent to the first surface and a crossbeam located adjacent to the second surface, whereby, when fire breaks out in the battery cell, it is possible to rapidly and accurately prevent spread of flames of the ignited battery cell.