To reliably detect the abnormality of a recycle fuel pipe that returns a part of fuel reformed by a reforming unit to a desulfurizer and suppress the degradation of the reforming unit and the failure of a fuel cell due to a sulfur component. Provided is a fuel cell system in which a recycle gas pipe 39 is provided with a temperature sensor 39a which directly detects the temperature of a recycle gas and a control device 15 detects the passage and/or the flow rate of the recycle gas passing through the recycle gas pipe 39 based on the temperature of the recycle gas detected by the temperature sensor 39a (a detection portion: step S108).
