A battery pack, comprising: 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 therethrough 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, wherein the pack casing includes: a casing body having a plurality of horizontal partitions and vertical partitions to form an accommodation space in which the battery cell assembly is accommodated; a casing cover provided at an upper surface of the casing body; and an elastic pressing unit provided on the casing cover to elastically press the battery cell assembly; and said casing body is depressed with a slope or at a right angle corresponding to a planar surface of the battery cell to form a placing groove in which the battery cell assembly is placed, said elastic pressing unit has a pair of inclined regions and a depressed region connecting ends of the inclined regions to be depressed from a planar surface of the casing cover, and said at least a part of the depressed region of the elastic pressing unit supports in contact with a top surface of the battery cell assembly to press the battery cell downwards. 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 therethrough 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, wherein the pack casing includes: a casing body having a plurality of horizontal partitions and vertical partitions to form an accommodation space in which the battery cell assembly is accommodated; a casing cover provided at an upper surface of the casing body; and an elastic pressing unit provided on the casing cover to elastically press the battery cell assembly; and said casing body is depressed with a slope or at a right angle corresponding to a planar surface of the battery cell to form a placing groove in which the battery cell assembly is placed, said elastic pressing unit has a pair of inclined regions and a depressed region connecting ends of the inclined regions to be depressed from a planar surface of the casing cover, and said at least a part of the depressed region of the elastic pressing unit supports in contact with a top surface of the battery cell assembly to press the battery cell downwards. a casing body having a plurality of horizontal partitions and vertical partitions to form an accommodation space in which the battery cell assembly is accommodated; a casing cover provided at an upper surface of the casing body; and an elastic pressing unit provided on the casing cover to elastically press the battery cell assembly; and said casing body is depressed with a slope or at a right angle corresponding to a planar surface of the battery cell to form a placing groove in which the battery cell assembly is placed, said elastic pressing unit has a pair of inclined regions and a depressed region connecting ends of the inclined regions to be depressed from a planar surface of the casing cover, and said at least a part of the depressed region of the elastic pressing unit supports in contact with a top surface of the battery cell assembly to press the battery cell downwards.