A control apparatus which is configured to control a fuel cell unit provided with a power generation unit which generates power upon chemical reaction and auxiliaries which assists an operation of the power generation unit, comprising: a control unit which is configured to instruct an operation mode of the fuel cell unit, to the fuel cell unit, wherein the operation mode of the fuel cell unit includes: a constant temperature mode for performing a control to cover power consumption of the auxiliaries by grid power and a control to keep a temperature of the power generation unit constant within a predetermined temperature range, where the power output from the power generation unit is smaller than the power consumption of the auxiliaries; and a self-support mode for performing a control to cover the power consumption of the auxiliaries by power different from the grid power, wherein the power is supplied by the power generation unit, a photovoltaic unit and/or a storage battery unit, wherein the self-support mode is a mode not to provide the power output from the power generation unit to a load connected to the fuel cell unit and to keep a temperature at a power generation temperature, wherein the predetermined temperature range in the constant temperature mode is lower than the power generation temperature in the self-support mode, characterized in that the control unit is configured to instruct to change the operation mode of the fuel cell unit to the self-support mode when a grid power failure occurs while the fuel cell unit is operating in the constant temperature mode, wherein the control unit is capable of controlling a distributed power supply unit capable of supplying the fuel cell unit with power, wherein the distributed power supply unit comprises the photovoltaic unit and/or the storage battery unit, and the control unit is configured to control the distributed power supply unit to cover, for a predetermined period, the power consumption of the auxiliaries by the power output from the distributed power supply unit, when instructing the self-support mode in response to a power failure occurs while the fuel cell unit is operated in the constant temperature mode, wherein the predetermined period is a period during which fuel supplied to the power generation unit increases. a control unit which is configured to instruct an operation mode of the fuel cell unit, to the fuel cell unit, wherein the operation mode of the fuel cell unit includes: a constant temperature mode for performing a control to cover power consumption of the auxiliaries by grid power and a control to keep a temperature of the power generation unit constant within a predetermined temperature range, where the power output from the power generation unit is smaller than the power consumption of the auxiliaries; and a self-support mode for performing a control to cover the power consumption of the auxiliaries by power different from the grid power, wherein the power is supplied by the power generation unit, a photovoltaic unit and/or a storage battery unit, wherein the self-support mode is a mode not to provide the power output from the power generation unit to a load connected to the fuel cell unit and to keep a temperature at a power generation temperature, wherein the predetermined temperature range in the constant temperature mode is lower than the power generation temperature in the self-support mode, characterized in that the control unit is configured to instruct to change the operation mode of the fuel cell unit to the self-support mode when a grid power failure occurs while the fuel cell unit is operating in the constant temperature mode, wherein the control unit is capable of controlling a distributed power supply unit capable of supplying the fuel cell unit with power, wherein the distributed power supply unit comprises the photovoltaic unit and/or the storage battery unit, and the control unit is configured to control the distributed power supply unit to cover, for a predetermined period, the power consumption of the auxiliaries by the power output from the distributed power supply unit, when instructing the self-support mode in response to a power failure occurs while the fuel cell unit is operated in the constant temperature mode, wherein the predetermined period is a period during which fuel supplied to the power generation unit increases. the control unit is capable of controlling a distributed power supply unit capable of supplying the fuel cell unit with power, wherein the distributed power supply unit comprises the photovoltaic unit and/or the storage battery unit, and the control unit is configured to control the distributed power supply unit to cover, for a predetermined period, the power consumption of the auxiliaries by the power output from the distributed power supply unit, when instructing the self-support mode in response to a power failure occurs while the fuel cell unit is operated in the constant temperature mode, wherein the predetermined period is a period during which fuel supplied to the power generation unit increases.