A solid oxide fuel cell device, in which fuel is supplied to fuel cell units and the remaining fuel flown out from one end of the fuel cell units is combusted to heat a reformer, the solid oxide fuel cell device comprising: a fuel cell module including plurality of fuel cell units in which fuel electrodes are formed in internal passages for passing fuel; a reformer disposed above the plurality of fuel cell units within the fuel cell module, for producing hydrogen by a partial oxidation reforming reaction resulting from the chemical reaction of fuel and reforming oxidant gas and a steam reforming reaction resulting from the chemical reaction of fuel and reforming steam; a vaporization chamber disposed above the plurality of fuel cell units and adjacent to the reformer, for vaporizing supplied water; a combustion chamber disposed inside the fuel cell module, that combusts fuel passed through the internal passage at the top end of each of the fuel cell units to heat the reformer and vaporization chamber above; a fuel supply device that, by supplying fuel to the reformer, feeds fuel reformed in the reformer into each of the fuel cell units; a reforming oxidant gas supply device that supplies reforming oxidant gas to the reformer; a water supply device that supplies reforming water to the vaporization chamber; a supply device of oxidant gas for electrical generation that supplies oxidant gas for electrical generation to the oxidant gas electrodes of the plurality of fuel cell units; and a controller programmed to control the fuel supply device, the supply device of oxidant gas for electrical generation, and the water supply device in a startup step of the fuel cell module to create a partial oxidation reforming reaction and a steam reforming reaction in the reformer, in order to raise the temperature of the plurality of fuel cell units to the temperature at which electrical generation is possible; characterized in that the fuel electrode of the each fuel cell unit is constituted to have a catalytic effect in a shift reaction in which hydrogen is produced from carbon monoxide and steam; wherein the controller is configured to execute only an ATR step and a SR step in the reformer; wherein in the ATR step, the partial oxidation reforming reaction and the steam reforming reaction occur simultaneously in the reformer, and in the SR step, only the steam reforming reaction occurs in the reformer, and wherein the supply of water by the water supply device is started before the temperature of the reformer reaches the temperature at which the partial oxidation reforming reaction occurs, so that the partial oxidation reforming reaction does not occur solely within the reformer. a fuel cell module including plurality of fuel cell units in which fuel electrodes are formed in internal passages for passing fuel; a reformer disposed above the plurality of fuel cell units within the fuel cell module, for producing hydrogen by a partial oxidation reforming reaction resulting from the chemical reaction of fuel and reforming oxidant gas and a steam reforming reaction resulting from the chemical reaction of fuel and reforming steam; a vaporization chamber disposed above the plurality of fuel cell units and adjacent to the reformer, for vaporizing supplied water; a combustion chamber disposed inside the fuel cell module, that combusts fuel passed through the internal passage at the top end of each of the fuel cell units to heat the reformer and vaporization chamber above; a fuel supply device that, by supplying fuel to the reformer, feeds fuel reformed in the reformer into each of the fuel cell units; a reforming oxidant gas supply device that supplies reforming oxidant gas to the reformer; a water supply device that supplies reforming water to the vaporization chamber; a supply device of oxidant gas for electrical generation that supplies oxidant gas for electrical generation to the oxidant gas electrodes of the plurality of fuel cell units; and a controller programmed to control the fuel supply device, the supply device of oxidant gas for electrical generation, and the water supply device in a startup step of the fuel cell module to create a partial oxidation reforming reaction and a steam reforming reaction in the reformer, in order to raise the temperature of the plurality of fuel cell units to the temperature at which electrical generation is possible; characterized in that the fuel electrode of the each fuel cell unit is constituted to have a catalytic effect in a shift reaction in which hydrogen is produced from carbon monoxide and steam; wherein the controller is configured to execute only an ATR step and a SR step in the reformer; wherein in the ATR step, the partial oxidation reforming reaction and the steam reforming reaction occur simultaneously in the reformer, and in the SR step, only the steam reforming reaction occurs in the reformer, and wherein the supply of water by the water supply device is started before the temperature of the reformer reaches the temperature at which the partial oxidation reforming reaction occurs, so that the partial oxidation reforming reaction does not occur solely within the reformer.