NOVELTY - Fuel cell (11) system comprises fuel processor (10) which produces fuel gas (9) which chemically reacts source gas and contains hydrogen, source gas path (12), desulfurizer (13), flow regulating valve (14) provided in the source gas path, flow meter (16) for measuring flow volume of the source gas, gas pump (15) which is provided in the source gas path and pumps the source gas to the fuel processor, control unit (17) which controls the flow regulating valve and gas pump, and filter (19) in exit unit (18) of the source gas in the desulfurizer.    USE - The system is useful for producing fuel gas and electric power.    ADVANTAGE - The system removes sulfur compound in the source gas which exerts deterioration effect on furl processor. While source gas supply amount to the fuel cell is stabilized, regular maintenance of desulfurizer can be made.    DETAILED DESCRIPTION - Fuel cell (11) system comprises fuel processor (10) which produces fuel gas (9) which chemically reacts source gas and contains hydrogen, source gas path (12) into which the source gas supplied to the fuel processor flows, desulfurizer (13) from which the sulfur compound which is provided in the source gas path and contained in source gas is removed, flow regulating valve (14) provided in the source gas path, flow meter (16) for measuring flow volume of the source gas, gas pump which is provided in the source gas path and pumps the source gas to the fuel processor, control unit (17) which controls the flow regulating valve and gas pump based on the flow volume of the source gas measured in the flow meter is provided, and filter (19) in exit unit (18) of the source gas in the desulfurizer.    DESCRIPTION OF DRAWING(S) - The drawing shows a block diagram showing structure of furl cell system.    Fuel gas (9)    Fuel processor (10)    Fuel cell (11)    Source gas path (12)    Desulfurizer (13)    Flow regulating valve (14)    Gas valve (15)    Flow meter (16)    Control unit (17)    Exit unit (18)    Filter (19)