Oxidant gas flows to the fuel cell stack through an oxidant gas supply channel. Oxidant off-gas is discharged from the fuel cell stack through an oxidant off-gas exhaust channel. A refrigerant is discharged from the fuel cell stack through a refrigerant exhaust channel. An outlet sealing valve is provided in the oxidant off-gas exhaust channel. The outlet sealing valve includes a main body, a valve seat, a valve body, and a refrigerant passage. The main body has a passage through which the oxidant off-gas flows. The valve seat is provided in the passage. The valve body is provided in the passage to be seated on the valve seat to close the passage. The refrigerant passage is branched off from the refrigerant exhaust channel. The refrigerant flows in a vicinity of at least one of the valve seat and the valve body through the refrigerant passage.