An EMS (200) is provided with a control unit (230) for instructing a fuel cell unit (150) to operate in one of operation modes including an idling mode for performing a control to cover power consumption of auxiliaries by power other than grid power, and a constant temperature mode for performing a control to cover the power consumption of the auxiliaries by power supplied from the outside and keep a temperature of a cell stack (51B) within a predetermined temperature range. When a power failure occurs while the fuel cell unit (150) is operating in the constant temperature mode, the control unit (230) controls the fuel cell unit (150) to operate in the idling mode.