A fuel cell system comprising: a fuel cell; a fuel treating unit configured to treat raw fuel and generate fuel gas for the fuel cell; an oxidant-gas heater configured to heat oxidant gas for the fuel cell; a combustor configured to combust the raw fuel and generate combustion gas to heat the fuel treating unit and the oxidant-gas heater; a first fuel injector configured to adjust a flow rate of the raw fuel supplied to the fuel treating unit; a second fuel injector configured to adjust a flow rate of the raw fuel supplied to the combustor; and a control unit configured to control the first fuel injector and the second fuel injector, wherein the control unit is configured to: execute warming-up of the fuel cell by controlling the first fuel injector and the second fuel injector, and execute rated operation of the fuel cell wherein the rated operation refers to an operation of the fuel cell at a maximum power-generation output, and is a power generation of the fuel cell for supplying power to an external device executed by activating the first fuel injector and stopping the second fuel injector after warming-up of the fuel cell; wherein the fuel cell system is configured to heat the raw fuel at the fuel treating unit with the combustion gas generated at the combustor as the heat source to promote the treatment of the raw fuel, and to heat the oxidant gas at the oxidant-gas heater to promote the warming-up of the fuel cell; characterized in that the control unit is configured to: set a raw-fuel total flow rate of the flow rate of the raw fuel for the first injector and the flow rate of the raw fuel for the second fuel injector during warming-up of the fuel cell such that the raw-fuel total flow rate is greater than the flow rate of the raw fuel in the first fuel injector during the rated operation, set the flow rate of the raw fuel for the second fuel injector to the raw-fuel total flow rate while the first fuel injector is set to be stopped before that the fuel treating unit reaches an operable temperature of the fuel treating unit, and set the flow rate of the raw fuel for the first fuel injector and the flow rate of the raw fuel for the second fuel injector such that the sum of the flow rate of the raw fuel for the first fuel injector and the flow rate of the raw fuel for the second fuel injector is set to be the raw-fuel total flow rate when the fuel treating unit reaches the operable temperature of the fuel treating unit. a fuel cell; a fuel treating unit configured to treat raw fuel and generate fuel gas for the fuel cell; an oxidant-gas heater configured to heat oxidant gas for the fuel cell; a combustor configured to combust the raw fuel and generate combustion gas to heat the fuel treating unit and the oxidant-gas heater; a first fuel injector configured to adjust a flow rate of the raw fuel supplied to the fuel treating unit; a second fuel injector configured to adjust a flow rate of the raw fuel supplied to the combustor; and a control unit configured to control the first fuel injector and the second fuel injector, wherein the control unit is configured to: execute warming-up of the fuel cell by controlling the first fuel injector and the second fuel injector, and execute rated operation of the fuel cell wherein the rated operation refers to an operation of the fuel cell at a maximum power-generation output, and is a power generation of the fuel cell for supplying power to an external device executed by activating the first fuel injector and stopping the second fuel injector after warming-up of the fuel cell; execute warming-up of the fuel cell by controlling the first fuel injector and the second fuel injector, and execute rated operation of the fuel cell wherein the rated operation refers to an operation of the fuel cell at a maximum power-generation output, and is a power generation of the fuel cell for supplying power to an external device executed by activating the first fuel injector and stopping the second fuel injector after warming-up of the fuel cell; set a raw-fuel total flow rate of the flow rate of the raw fuel for the first injector and the flow rate of the raw fuel for the second fuel injector during warming-up of the fuel cell such that the raw-fuel total flow rate is greater than the flow rate of the raw fuel in the first fuel injector during the rated operation, set the flow rate of the raw fuel for the second fuel injector to the raw-fuel total flow rate while the first fuel injector is set to be stopped before that the fuel treating unit reaches an operable temperature of the fuel treating unit, and set the flow rate of the raw fuel for the first fuel injector and the flow rate of the raw fuel for the second fuel injector such that the sum of the flow rate of the raw fuel for the first fuel injector and the flow rate of the raw fuel for the second fuel injector is set to be the raw-fuel total flow rate when the fuel treating unit reaches the operable temperature of the fuel treating unit.