An SOFC system is started-up efficiently in a short time while letting a hydrogen concentration in a reformed gas high. A method for starting-up an SOFC system including a reformer having a reforming catalyst, and an SOFC which uses the reformed gas as a fuel, in which, catalyst A having POX function and catalyst B having SR function are used as the reforming catalyst, the method including the steps of: increasing the temperature of catalyst A, by combustion heat or electricity, to a temperature at which POX reaction can proceed; increasing the temperature of catalyst B by POX reaction heat, increasing the temperature of SOFC by feeding the reformed gas to an anode and heating catalyst B by combustion heat generated from combustion of a reformed gas discharged from the anode, or increasing the temperature of catalyst B by POX reaction heat, increasing the temperature of SOFC by feeding a combustion gas produced from combustion of the reformed gas to a cathode and heating catalyst B by this combustion gas; and reducing the proportion of POX reaction or stopping POX reaction and perform SR, after catalyst B is heated to a temperature at which SR reaction can proceed.