PURPOSE: To obtain the captioned gas separator having large mechanical strength and excellent in the heat-proof cycling properties by using a porous body having the specific minute hole diameter as a separating film, which sepatates hydrogen in exhaust gas.

CONSTITUTION: A porous body having a minute hole diameter 10∼8,000 is formed a separating film, which separates hydrogen from the mixed gas containing hydrogen. For instance, a gas separator 1 is provided with a cylindrical separating film 9, which forms a mixed gas chamber 7 and a hydrogen chamber 8 in a container 6, whose both ends are airtightly blocked by end plates 4 and 5 through block members 2 and a packing 3. The separating film 9 is made of, for instance, porous glass having the minute hole diameter 50, a porosity rate 30% and the thickness 2mm, whereby one end of said separating film is held by the supporting part 10 provided on the upper side end plate 4, while the other end is held by the supporting member 12 provided on the central part of a nipple 11, which is screwed into the central hole of the lower side end plate 5 for blocking. Further, a gas inlet 13 leading to the mixed gas chamber 7 is provided near the upper end of the container 6, while a gas outlet 14 leading to the mixed gas chamber 7 is provided inside the lower end plate 5, still further a hydrogen outlet 15 leading to the hydrogen chamber 8 is provided inside the supporting member 12.