NOVELTY - A fuel cell stack comprises two end plates (110), current collectors (112, 113), membrane electrode assembly, and connecting device (140). The two end plates are arranged to be opposite to each other with a predetermined interval between them. The first current collectors respectively contacts insides of the end plates. The second current collectors respectively contact the first current collectors. The second current collectors have a coefficient of thermal expansion greater than that of the first current collectors.    USE - A fuel cell stack used in vehicles.    ADVANTAGE - The fuel cell stack has enhanced stability during cold start using resistivity of double current collectors with different coefficient of thermal expansion. The fuel cell stack eliminates increased in thickness. The fuel cell stack minimizes performance deviation due to temperature variations among cells which is generated while operating fuel cell stack at low temperature less than 0degrees C, thus improving stability of fuel cell.    DETAILED DESCRIPTION - A fuel cell stack comprises two end plates (110), current collectors (112, 113), membrane electrode assembly, and connecting device (140). The two end plates are arranged to be opposite to each other with a predetermined interval between them. The first current collectors respectively contacts insides of the end plates. The second current collectors respectively contact the first current collectors. The second current collectors have a coefficient of thermal expansion greater than that of the first current collectors. The third current collectors selectively contact the second current collectors depending on a surrounding temperature. The separators respectively contact an inside of the third current collectors. The membrane electrode assembly contacts the separators and disposed alternately with the separators to form a stack where cells are piled up. The connecting device encompasses the two end plates and units arranged between the two end plates. The fuel cell stack includes guide part, and bending prevention bar.    DESCRIPTION OF DRAWING(S) - The figure shows a drawing illustrating change in current collector at low and high temperatures.    End plates (110)    Current collectors (112, 113)    Separator (120)    Connecting device (140)