A solid oxide fuel cell system comprising: a fuel cell module including a fuel cell stack configured to cause a reaction between a reformed gas and electric power generation air to generate electric power, the reformed gas being generated by reforming a raw material, a reformer portion configured to reform the raw material to generate the reformed gas, an igniting portion configured to ignite the raw material when starting up the solid oxide fuel cell system, and a combustor that is a space where the raw material ignited by the igniting portion is combusted together with the electric power generation air; a raw material supply portion configured to supply the raw material to the fuel cell module; an electric power generation air supply portion configured to supply the electric power generation air to the fuel cell module; a reforming air supply portion configured to supply reforming air to the reformer portion; a water supply portion configured to supply reforming water to the reformer portion; an exhaust gas purifying portion configured to purify a flue gas generated by the combustion in the combustor; a flow rate controller (14, 15, 16, 17) configured to control flow rates of the raw material, the reforming air, the electric power generation air, and the reforming water; a purifying portion temperature detector provided at an inlet of the exhaust gas purifying portion and configured to detect a temperature of the inlet of the exhaust gas purifying portion; and a main controller, wherein after the temperature of the inlet of the exhaust gas purifying portion detected by the purifying portion temperature detector becomes a predetermined temperature after the ignition, the main controller is configured to cause the water supply portion and the flow rate controller (14, 15, 16, 17) to increase the flow rate of the reforming water to the reforming portion. a fuel cell module including a fuel cell stack configured to cause a reaction between a reformed gas and electric power generation air to generate electric power, the reformed gas being generated by reforming a raw material, a reformer portion configured to reform the raw material to generate the reformed gas, an igniting portion configured to ignite the raw material when starting up the solid oxide fuel cell system, and a combustor that is a space where the raw material ignited by the igniting portion is combusted together with the electric power generation air; a fuel cell stack configured to cause a reaction between a reformed gas and electric power generation air to generate electric power, the reformed gas being generated by reforming a raw material, a reformer portion configured to reform the raw material to generate the reformed gas, an igniting portion configured to ignite the raw material when starting up the solid oxide fuel cell system, and a combustor that is a space where the raw material ignited by the igniting portion is combusted together with the electric power generation air; a raw material supply portion configured to supply the raw material to the fuel cell module; an electric power generation air supply portion configured to supply the electric power generation air to the fuel cell module; a reforming air supply portion configured to supply reforming air to the reformer portion; a water supply portion configured to supply reforming water to the reformer portion; an exhaust gas purifying portion configured to purify a flue gas generated by the combustion in the combustor; a flow rate controller (14, 15, 16, 17) configured to control flow rates of the raw material, the reforming air, the electric power generation air, and the reforming water; a purifying portion temperature detector provided at an inlet of the exhaust gas purifying portion and configured to detect a temperature of the inlet of the exhaust gas purifying portion; and a main controller, wherein after the temperature of the inlet of the exhaust gas purifying portion detected by the purifying portion temperature detector becomes a predetermined temperature after the ignition, the main controller is configured to cause the water supply portion and the flow rate controller (14, 15, 16, 17) to increase the flow rate of the reforming water to the reforming portion.