A fuel cell system according to the present invention comprises: a fuel cell (1); an auxiliary machine; a sensor for detecting an operation state of the fuel cell system; an auxiliary machine failure detection means (44) for detecting a failure of the auxiliary machine; a sensor output abnormality detecting means (45) for detecting an abnormality of the operation state of the fuel cell system, and a controller (47). When the fuel cell system is normally operated, if the auxiliary machine failure detection means (44) detects a failure and the sensor output abnormality detecting means (45) does not detect an abnormality and if the auxiliary machine failure detection means (44) does not detect a failure and the sensor output abnormality detecting means (45) does not detect an abnormality, the controller controls the operation of the fuel cell system to be continued; if the auxiliary machine failure detection means (44) detects a failure and the sensor output abnormality detecting means (45) detects an abnormality and if the auxiliary machine failure detection means (44) does not detect a failure and the sensor output abnormality detecting means (45) detects an abnormality, the controller controls the operation of the fuel cell system to be stopped.
