NOVELTY - A catalyst A comprises catalyst precursor reduced by copper-aluminate spinel-type complex oxide containing titanium or zinc, less than or equal to 5% of oxide with respect to cuprous aluminate (CuAlO2) and each strongest line diffraction intensity of copper alumina (Al2O3), and metal copper particles which is embedded at oxide and is dispersed. The copper-aluminate spinel-type complex oxide is cupric aluminate (CuAl2O4) and copper alumina (CuAl2O3) in which diffraction intensity of (311) plane of surface layer part is strongest line in X-ray diffraction.    USE - A catalyst for modifier used for fuel cell system (claimed).    ADVANTAGE - The catalyst is excellent in oxidation resistance, sintering-proof property and adhesiveness of base material and metal particle, has long life, and is inexpensive.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) a catalyst B comprising catalyst A and solid acid catalyst which are mixed;    (2) a modifier A comprising catalyst A and B, carrying body which carries catalyst, and container which accommodates carrier which carried catalyst in which fuel and water vapor which are supplied from outside are made to react within container and hydrogen from reaction material are removed;    (3) a fuel cell system A comprising fuel cell, modifier A, and hydrogen supply path which supplies hydrogen removed with modifier to fuel cell;    (4) a catalyst C comprising catalyst precursor reduced by copper-aluminate spinel-type complex oxide containing titanium or zinc, less than or equal to 5% of oxide with respect to cuprous aluminate (CuAlO2) and each strongest line diffraction intensity of copper alumina (Al2O3), metal copper particles which is embedded at oxide and is dispersed, and metal cobalt particles which is embedded at oxide and is dispersed;    (5) a catalyst D comprising solid acid catalyst and catalyst C;    (6) a modifier B comprising catalyst C and catalyst D; and    (7) a fuel cell system B comprising modifier B, fuel cell, and hydrogen supply path which supplies hydrogen removed with modifier to fuel cell.    DESCRIPTION OF DRAWING(S) - The drawing shows a sectional view of hydrocarbon fuel modifier.    Tank (10)    Modifier tank (20)    Preheating apparatus (30, 40)    Mixer (50)    Container (60)    Burner (70)    Reforming-catalyst layer (80)