NOVELTY - The gas separation apparatus (6) separates and ejects specific gas introduced into the casings (26,28). The chamber (21) supports both ends of hollow gas separation film (14) and separated gas is ejected through the chamber (22). Purge gas is introduced into the chamber (23). The chambers (22,23) face each of the both ends (14a,14b) where the film is opened wide. The chambers are maintained airtight.    USE - Hydrogen gas separation apparatus used for fuel cell system for motor vehicles, etc.    ADVANTAGE - The purge of residual gas in the gas separation film is performed completely in a short time. Damage of the gas separation film is prevented by absorbing the thermal expansion and tensile load on the film by moving the flange. The cost is reduced. The load acting on the separation film is set to zero form the time of starting of the fuel cell system till stopping during purge, by offsetting the flange and adjusting the introductory pressure of remaining gas. The durability of O-ring is increased by preventing thermal deterioration by providing cooling device.    DETAILED DESCRIPTION - The gas separation apparatus (6) separates and ejects specific gas introduced into the casing. The chamber (21) is demarcated by the inner wall of the flanges (16,18). The flange (18) and the inner wall of the casing (28) demarcates the chamber (22). The wall of the flange (16) and the casing (26) demarcates the chamber (23). The hollow fiber-like gas separation film follows axially and the flange (18) is provided movably along the chamber (21) by a coil spring or piping. The pneumatic energizer introduces remaining gas ejected from the chamber (21) into the chamber (22) as backing pressure opposing the flange (18). The coil spring energizes the pressure of the introduction gas which is approximately half to the flange (18). O-ring (30) which air tightly insulates the chamber (21) is provided to the flange (18). The O-ring is cooled by bellows provided to the casing.    An INDEPENDENT CLAIM is also included for fuel cell system for motor vehicles which has gas separation apparatus.    DESCRIPTION OF DRAWING(S) - The figure shows the sectional view of the gas separation apparatus. (Drawing includes non-English text).    Gas separation apparatus (6)    Gas separation film (14)    Ends (14a,14b)    Flanges (16,18)    Chambers (21-23)    Casings (26,28)    O-ring (30)