Disclosed is a battery pack, which includes a battery cell assembly having at least one battery cell; a pack casing having an input port and an output port provided at one side thereof so that a coolant flows in and out to cool the battery cell, the pack casing accommodating the battery cell assembly to fix and support the battery cell assembly; and a coolant supply and circulation unit connected to communicate with the input port and the output port to supply and circulate the coolant into the pack casing so that each battery cell is cooled in contact with the coolant.