NOVELTY - The system has a cooling water circulating loop cooling a fuel cell stack, where cooling water passing through the stack is introduced to cooling water channels (150, 160) via cooling water introducing ports (140a, 140b). Cooling water discharging ports (140c, 140d) correspond to the cooling water introducing ports, where the cooling water is discharged through the discharging ports. The cooling water channels connect the introducing and discharging ports, where cooling water flows in different directions on the water channels. The channels are alternately placed between adjacent fuel cells.    USE - Fuel cell system for cooling heat generated in a rectangular cross-sectioned fuel cell stack upon producing electric energy in a fuel cell for a vehicle e.g. hybrid vehicle, electric vehicle, plug-in hybrid electric vehicle, hydrogen- powered vehicle, diesel-powered and electric-powered vehicle, and motor vehicle such as passenger automobiles e.g. sports utility vehicle, bus, lorry, commercial vehicle, watercraft such as boats and ships, and aircraft. Can also be used for industry, home, and small-sized electric/electronic product.    ADVANTAGE - The system improves output performance and the durability of the stack by reducing a temperature difference between a section through which cooling water is introduced and another section through which the cooling water is discharged along the flow direction of the cooling water, thus preventing local reduction of efficiency by providing cooling water channels formed such that the cooling water flows in different directions. The system reduces a temperature deviation generated when heat of cooling water circulating in a cooling system is exchanged in a stack so as to achieve a desired cooling effect. The system allows temperature deviation to be removed by alternating the flow directions of cooling water passages in directions, thus offsetting the temperature gradient generated by heat transfer as the cooling water flows through the cooling channels.    DESCRIPTION OF DRAWING(S) - The drawing shows an exploded perspective view of cooling water channels in a fuel cell cooling system for a vehicle.    Anode bipolar plate (110)    Membrane electrode assembly (120)    Cathode bipolar plate (130)    Cooling water introducing ports (140a, 140b)    Cooling water discharging ports (140c, 140d)    Cooling water channels (150, 160)