A fuel cell device for generating power by using fuel being reformed by a reformer, said fuel cell device comprising: means for supplying fuel to the reformer; means for supplying reforming air to the reformer; means for producing pure water and supplying the pure water to the reformer; fuel supply flow rate detection means for detecting the flow rate of fuel supplied by the fuel supply means; air supply flow rate detection means for detecting the flow rate of reforming air supplied by the reforming air supply means; water supply flow rate detection means for detecting the flow rate of water supplied by the water supply means; and control means (52; 110) configured to control, at the time of startup of the fuel cell device, the flow rate of fuel supplied by the fuel supply means, the flow rate of reforming air supplied by the reforming air supply means, and the flow rate of water supplied by the water supply means to supply fuel and reforming air into the reformer so as to conduct a partial oxidation reforming reaction, then to supply fuel, reforming air, and water into the reformer to conduct an auto-thermal reforming reaction, then to supply fuel and water into the reformer to conduct a steam reforming reaction; wherein the water supply means is configured to intermittently supply water to the reformer under pulsed control; the control means (52; 110) is configured to control the fuel supply means, the reforming air supply means, and the water supply means respectively to supply target supply flow rates of fuel, reforming air, and water based on the respective outputs of the fuel supply flow rate detection means, the reforming air supply flow rate detection means, and the water supply flow rate detection means; and the control means (52; 110), in the auto-thermal reforming reaction region, is configured to suppress changes in the flow rate of fuel supplied by the fuel supply means during at least a predetermined interval following the supply of water by the water supply means. means for supplying fuel to the reformer; means for supplying reforming air to the reformer; means for producing pure water and supplying the pure water to the reformer; fuel supply flow rate detection means for detecting the flow rate of fuel supplied by the fuel supply means; air supply flow rate detection means for detecting the flow rate of reforming air supplied by the reforming air supply means; water supply flow rate detection means for detecting the flow rate of water supplied by the water supply means; and control means (52; 110) configured to control, at the time of startup of the fuel cell device, the flow rate of fuel supplied by the fuel supply means, the flow rate of reforming air supplied by the reforming air supply means, and the flow rate of water supplied by the water supply means to supply fuel and reforming air into the reformer so as to conduct a partial oxidation reforming reaction, then to supply fuel, reforming air, and water into the reformer to conduct an auto-thermal reforming reaction, then to supply fuel and water into the reformer to conduct a steam reforming reaction; wherein the water supply means is configured to intermittently supply water to the reformer under pulsed control; the control means (52; 110) is configured to control the fuel supply means, the reforming air supply means, and the water supply means respectively to supply target supply flow rates of fuel, reforming air, and water based on the respective outputs of the fuel supply flow rate detection means, the reforming air supply flow rate detection means, and the water supply flow rate detection means; and the control means (52; 110), in the auto-thermal reforming reaction region, is configured to suppress changes in the flow rate of fuel supplied by the fuel supply means during at least a predetermined interval following the supply of water by the water supply means.