NOVELTY - A hydrogen gas separator fixing structure includes a metal flange (4, 14) connected to open end(s) of a gas separator (7). A bonding layer (5) having a thickness of 20-400 microns is provided at a portion at which gas separator and metal flange are connected to each other and on the surface of gas separation membrane (8) side of the portion. A packing (6) is provided on the bonding layer. A metal mechanism (1, 11) capable of fixing the packing by pressing is provided so that its part is in contact with the bonding layer.    USE - For use in e.g. hydrogen purifier for fuel cell and apparatus for hydrogen production by steam reforming using hydrocarbons as raw material.    ADVANTAGE - The hydrogen gas separator fixing structure hardly gives rise to thermal stress-induced breakage of a substrate constituting the gas separator and to reduction in gas tightness between gas separator and metal flange, caused by the load of heat cycle, and can be used even at high temperature.    DETAILED DESCRIPTION - A hydrogen gas separator fixing structure includes a gas separator comprising a tubular support (9) and a gas separation membrane provided on support surface(s) and containing first metal capable of separating hydrogen gas from hydrogen-containing gas. A metal flange is connected to open end(s) of gas separator. A bonding layer of second metal having a thickness of 20-400 microns is provided at the portion at which gas separator and metal flange are connected to each other and on the surface of gas separation membrane side of the portion. The bonding layer is provided on the surface of gas separation membrane side of the portion by heat treatment at a temperature lower (preferably by greater than or equal to50degreesC) than the melting point of second metal. A packing is provided on the bonding layer. A metal mechanism capable of fixing the packing by pressing is provided so that its part is in contact with the bonding layer. An INDEPENDENT CLAIM is included for a hydrogen gas separating device.    DESCRIPTION OF DRAWING(S) - The figure is a schematic sectional view of a hydrogen gas separator fixing structure.    Metal mechanism (1, 11)    Packing presser (2, 12)    Stopper (3, 13)    Metal flange (4, 14)    Bonding layer (5)    Packing (6)    Gas separator (7)    Gas separation membrane (8)    Tubular support (9)    Stuffing box (15)    Thread groove (16)    Through-hole (21)