TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Arrangement: Bypass unit (23) supplies raw fuel gas to the desulfurizer without going through the dehumidifier, when the regenerator supplies resurgent gas to the dehumidifier. The regenerator supplies resurgent gas to the dehumidifier when the temperature of adsorbent, temperature of raw fuel gas, or external temperature exceeds preset value. The regenerator supplies resurgent gas to the dehumidifier when the temperature-increase rate of the adsorbent is less than preset value. Bypass unit (24) supplies air exhausted from the dehumidifier to the cathode (71) of a fuel cell (70). A flow-path form selection unit (24) selects flow-path form (I) which supplies raw fuel gas to the cathode without going through the dehumidifier and desulfurizer, and modifier and air going through the dehumidifier and desulfurizer, and flow-path form (II) which supplies modifier to the cathode without going through the desulfurizer, raw fuel gas without going through the dehumidifier, and air going through the desulfurizer and dehumidifier, based on the temperature-increase rate of the adsorbent within preset period immediately after selecting flow-path form (I). The regenerator supplies resurgent gas in which sulfur component partial pressure is lower than the raw fuel gas supplied to the dehumidifier to the desulfurizer, without going through the dehumidifier. When the resurgent gas is supplied to the desulfurizer, a discharge unit is provided for discharging the desulfurizer resurgent gas discharged from the desulfurizer to atmosphere. The regenerator is operated at conditions such that the odor of raw fuel gas discharged from the desulfurizer is below the odor detection limit, and the desulfurizer resurgent gas is supplied to the desulfurizer. The regenerator supplies desulfurizing resurgent gas to the desulfurizer when the required load of fuel cell to which hydrogen-containing gas is supplied is less than preset value. The resurgent gas is air or hot air.