TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Catalyst: The catalyst of the first catalyst layer comprises at least one selected from Pt and Pd, and a catalyst of the second catalyst layer comprises at least one selected from Ru, Rh and Ni.The carrier of the first catalyst layer comprises at least one selected from Al2O3 and zeolite, and a carrier of the second catalyst layer comprises at least one selected from Al2O3, SiO2, SiO2.Al2O3, MgO, TiO2 and zeolite.At least one of the first catalyst layer and the second catalyst layer comprises a catalyst, a carrier of the catalyst and a substrate having the catalyst and the carrier thereon, the substrate being in the form of honeycomb or foamed with communicating pores.The substrate is made of a metal or an inorganic material having high thermal conductivity.A certain space is provided between the first catalyst layer and the second catalyst layer, this certain space accommodates a heat-dissipating means or a cooling means therein.The first catalyst layer comprises several layers, and the hydrogen purifying apparatus further comprises an oxidant gas supplying unit for supplying oxidant gas to each of the layers.The first catalyst layer and the second catalyst layers are integrated onto one unit using a substrate in the form of honeycomb or a foamed substrate with communicating pores. EXAMPLE - A catalyst powder comprising 100 pts. wt. Al2O3 and 5 pts. wt. Pt dispersed on the Al2O3 was prepared. The catalyst powder was applied on a honeycomb substrate made of cordierite having a diameter of 100 mm and a length of 50 mm to form a first catalyst layer. Further, a catalyst powder comprising 100 pts. wt. Al2O3 and 5 pts. wt. Ru dispersed on the Al2O3 was prepared. The catalyst powder was applied on a honeycomb substrate made of cordierite having a diameter of 100 mm and a length of 50 mm to form a second catalyst layer. The obtained first and second catalyst layers were placed in the reaction chamber of a hydrogen purifying apparatus. A reformed gas comprising 1 volume % of CO. 15 volume % of carbon dioxide, 15 volume % of water vapor, and hydrogen of 69 volume % was introduced into the hydrogen purifying apparatus at a rate of 10 l/min from a reformed gas supplying unit. The reformed gas had been cooled to predetermined temperatures before reaching the reformed gas supplying unit. Air was supplied from an oxidant gas supplying unit so that oxygen concentration of the overall gas became 2 volume %. The composition of a purified gas discharged from a gas outlet was determined using gas chromatography after removal of water vapor therefrom. The CO concentration and the methane concentration of the gas were then calculated.