A fuel cell device comprising: a fuel cell that is connected to a system power supply and that generates power with a fuel gas and an oxygen containing gas; a plurality of auxiliaries used for the power generation of the fuel cell; a storage battery; an auxiliary power switching unit configured to switch power supplies to the respective auxiliaries from the storage battery; a power supply source switching unit configured to switch between the system power supply or the storage battery and the fuel cell as a power supply source to the auxiliaries; and a controlling device, wherein the controlling device is configured to control the auxiliary power switching unit and the power supply source switching unit such that, when the fuel cell device that is not operating is started up at a time of power failure of the system power supply, the controlling device is configured to: determine auxiliaries necessary for the startup and auxiliaries unnecessary for the startup; control the auxiliary power switching unit in such a way as to supply the power from the storage battery to only the auxiliary necessary for the startup; and thereafter control the power supply source switching unit in such a way that if a temperature of the fuel cell reaches a temperature at which driving power of the auxiliaries necessary for the startup is obtained, switching is performed to power supply from the fuel cell from power supply from the storage battery. a fuel cell that is connected to a system power supply and that generates power with a fuel gas and an oxygen containing gas; a plurality of auxiliaries used for the power generation of the fuel cell; a storage battery; an auxiliary power switching unit configured to switch power supplies to the respective auxiliaries from the storage battery; a power supply source switching unit configured to switch between the system power supply or the storage battery and the fuel cell as a power supply source to the auxiliaries; and a controlling device, wherein the controlling device is configured to control the auxiliary power switching unit and the power supply source switching unit such that, when the fuel cell device that is not operating is started up at a time of power failure of the system power supply, the controlling device is configured to: determine auxiliaries necessary for the startup and auxiliaries unnecessary for the startup; control the auxiliary power switching unit in such a way as to supply the power from the storage battery to only the auxiliary necessary for the startup; and thereafter control the power supply source switching unit in such a way that if a temperature of the fuel cell reaches a temperature at which driving power of the auxiliaries necessary for the startup is obtained, switching is performed to power supply from the fuel cell from power supply from the storage battery. determine auxiliaries necessary for the startup and auxiliaries unnecessary for the startup; control the auxiliary power switching unit in such a way as to supply the power from the storage battery to only the auxiliary necessary for the startup; and thereafter control the power supply source switching unit in such a way that if a temperature of the fuel cell reaches a temperature at which driving power of the auxiliaries necessary for the startup is obtained, switching is performed to power supply from the fuel cell from power supply from the storage battery.