NOVELTY - A de-sulfurizer (10) comprises de-sulfurizing portions (I,II) (13,14). De-sulfurizing portion (I) consists of de-sulfurizing agent (I) containing a catalytically active metal supported on a zeolite-type support, and is provided at the former-flow side of the fuel gas introduction line (12). De-sulfurizing portion (II) consists of de-sulfurizing agent (II) which removes the carbonyl sulfide in the gas (11) for fuel cells, and is provided at the later-flow side of the fuel gas introduction line.    USE - For fuel cell system (claimed).    ADVANTAGE - The de-sulfurizer efficiently removes carbonyl sulfide from fuel gas, and maintains high activity over a long period of time. The de-sulfurizer improves the electric-power-generation efficiency of fuel cell systems.    DETAILED DESCRIPTION - A de-sulfurizer (10) comprises de-sulfurizing portions (I,II) (13,14). De-sulfurizing portion (I) consists of de-sulfurizing agent (I) containing a catalytically active metal supported on a zeolite-type support, and is provided at the former-flow side of the fuel gas introduction line (12). De-sulfurizing portion (II) consists of de-sulfurizing agent (II) which removes the carbonyl sulfide in the gas (11) for fuel cells, and is provided at the later-flow side of the fuel gas introduction line. The de-sulfurizer installed on the fuel gas introduction line which introduces the fuel gas containing the sulfur compound, removes the sulfur compound from the fuel gas. INDEPENDENT CLAIMS are included for the following:    (1) de-sulfurization of hydrocarbon group fuel, which involves removing sulfur compounds in the hydrocarbon group fuel using the de-sulfurizer; and    (2) fuel cell system using a hydrocarbon group fuel and equipped with the de-sulfurizer. The de-sulfurized hydrocarbon group fuel is reformed by a reformer, and the reformed gas generates electric power in the fuel cell.    DESCRIPTION OF DRAWING(S) - The figure shows the schematic drawing of the de-sulfurizer. (Drawing includes non-English language text).    de-sulfurizer (10)    gas (11)    fuel gas introduction line (12)    de-sulfurization portions (13,14)    de-sulfurized fuel gas (15)