NOVELTY - An oxygen-permeating membrane (10) comprises first layer (12) which is formed of mixture of stabilized zirconia and electronic conductor which are oxygen ion conductors, 2nd layer (14) which is formed of mixture of cerium oxide and electronic conductor which have oxygen ion conductivity which dissolves rare earth elements with active substance, and is laminated on one side of 1st layer, and catalyst layer (16) which contains lanthanum compound and is arranged on surface different from surface in which 1st and 2nd layers are formed.    USE - An oxygen-permeating membrane used for modifier (claimed).    ADVANTAGE - Durability and performance are improved.    DETAILED DESCRIPTION - An oxygen-permeating membrane (10) comprises first layer (12) which is formed of mixture of stabilized zirconia and electronic conductor which are oxygen ion conductors, 2nd layer (14) which is formed of mixture of cerium oxide and electronic conductor which have oxygen ion conductivity which dissolves rare earth elements with active substance, and is laminated on one side of 1st layer, and catalyst layer (16) which contains lanthanum compound of formulae La1-xSrxFe1-yCoyO3-z and La1-xSrxMnO3-z and is arranged on surface different from surface in which 1st and 2nd layers are formed so that catalyst layer becomes high-oxygen part pressure side and 1st layer becomes low-oxygen part pressure side.    x,y=0-0.4; and    z=arbitrary.    An INDEPENDENT CLAIM is included for a modifier (20) comprising oxygen-permeating membrane which generates hydrogen from reformed fuel by partial-oxidation reaction, oxygen-containing gas flow path into which oxygen-containing gas for supplying catalyst layer side of oxygen-permeating membrane flows, and reformed fuel supply path which reformed fuel for supplying 1st layer side of oxygen-permeating membrane flows through and permeates oxygen permeating membrane.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional schematic view of the modifier with oxygen-permeating membrane.    Oxygen-permeating membrane (10)    First layer (12)    2nd layer (14)    Catalyst layer (16)    Modifier (20)