NOVELTY - A source gas passage (6) has desulfurizers (100,200) arranged in a relatively high and low temperature environments, while respectively exhibiting desulfurization performance relative to source gas having higher and lower dew points. The desulfurization performance of desulfurizer (200) relative to source gas having relatively higher dew point, is reduced. Source gas passage is equipped with a flowmeter (300) that measures source gas flow volume. The desulfurizers and flowmeters are arranged towards downstream side of source gas passage in source gas flow direction.    USE - Fuel cell system such as solid oxide fuel cell (SOFC) system, polymer electrolyte fuel cell (PEFC) system, phosphoric acid fuel cell (PAFC) system and molten carbonate fuel cell (MCFC) system, etc.    ADVANTAGE - Sulfur compound contained in source gas is appropriately desulfurized in a case where the source gas has a low dew point and a small volume of water vapor and in a case where the source gas has a high dew point and a large volume of water vapor. The flowmeter measuring the flow rate of the source gas is appropriately protected so as to contribute to a long lifetime of the flowmeter. The temperature of the source gas flowing to the flowmeter arranged at the downstream side of the desulfurizer is reduced.    DETAILED DESCRIPTION - The source gas passage is comprised of a buffer having a buffer chamber. The desulfurizers, flowmeter, buffer, and a gas supply source (60) are arranged at the source gas passage in a sequential arrangement order from the upstream side to the downstream side of the source gas passage in the flow direction of the source gas. The gas supply source, desulfurizers and flowmeter are arranged at source gas passage in a state where the arrangement order is the gas supply source, desulfurizers and the flowmeter from the upstream side to the downstream side of the source gas passage in the flow direction of source gas. Heat is received at a desulfurizer (100) from one of an insulated wall (19) that covers a reformer (2A), a fuel cell (1), and an exhaust gas passage through which an exhaust gas emitted from the reformer is passed. A hot water passage is provided through which hot water heated by a power generating operation of the fuel cell system is passed. A hot water storage tank is connected to the hot water passage, for storing hot water supplied from the hot water passage. The desulfurizer (100) is arranged in a temperature environment so as to receive heat from the hot water passage and the hot water storage tank.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of the fuel cell system.    Fuel cell (1)    Reformer (2A)    Source gas passage (6)    Insulated wall (19)    Desulfurizers (100,200)    Flowmeter (300)