FUEL CELL SYSTEM AND OPERATION METHOD THEREOF

A fuel cell system according to the present invention includes: a fuel cell (2); a fuel gas supply unit; an oxidizing gas supply unit; an oxidizing gas supply passage (13); an oxidizing gas discharge passage (14); an oxidizing gas branch passage (15) configured to branch from the oxidizing gas supply passage (13); an on-off valve disposed on at least one of the oxidizing gas discharge passage (14) and a portion of the oxidizing gas supply passage (13), the portion being located between the fuel cell (2) and a branched portion where the oxidizing gas branch passage (15) branches from the oxidizing gas supply passage (13); an oxidizing gas supply amount measuring unit disposed on the oxidizing gas branch passage (15); and a controller (20) configured to determine that the on-off valve is normal in a case where a supply amount of the oxidizing gas measured by the oxidizing gas supply amount measuring unit is equal to or larger than a first threshold when the controller has activated the oxidizing gas supply unit and output a close signal to the on-off valve and determines that the on-off valve is abnormal in a case where the supply amount of the oxidizing gas measured by the oxidizing gas supply amount measuring unit is smaller than the first threshold when the controller has activated the oxidizing gas supply unit and output the close signal to the on-off valve.