A solid oxide fuel cell system includes a fuel cell stack that generates electric power through a reaction between a fuel gas and an oxidizing gas; a combustor in which anode and cathode off-gases discharged from the fuel cell stack are burned by diffusion combustion; a temperature sensor that detects temperature of the anode off-gas flowing into the combustor; and a controller. When the system is in at least one of the following states during power generation, the controller instructs the system to perform a power-generation control action for preventing failed combustion reactions: the temperature of the anode off-gas, detected by the temperature sensor, is below a first predetermined temperature for a predetermined continuous period of time; the temperature of the anode off-gas decreases by not less than a predetermined second temperature range during a predetermined period of time.