Fuel cell vehicle detecting and controlling the H2-concentration in the exhaust gas

A fuel cell system comprises a fuel cell (1), a hydrogen discharge valve (6) for discharging hydrogen from the fuel cell (1) under a predetermined condition, a hydrogen concentration reduction device (10) for reducing the concentration of hydrogen discharged from the hydrogen discharge valve, a hydrogen sensor (45) for detecting an instantaneous hydrogen concentration of a gas processed by the hydrogen concentration reduction device and an average hydrogen concentration calculating unit for calculating an average hydrogen concentration per hour of a gas processed by the hydrogen concentration reduction device, wherein a hydrogen discharge from the fuel cell by the hydrogen discharge valve is prohibited in the event that an instantaneous hydrogen concentration detected by the hydrogen sensor (45) exceeds a first threshold, or in the event that an average hydrogen concentration calculated by the average hydrogen concentration calculating unit exceeds a second threshold which is lower than the first threshold.