A fuel cell system includes a fuel cell, an oxidant gas supply piping, an oxidant gas discharge piping, an air compressor, a turbine, a pressure regulating valve, and a check valve. The fuel cell generates electric power through an electrochemical reaction between a fuel gas and an oxidant gas. The oxidant gas supply piping is connected to the fuel cell. The oxidant gas discharge piping is connected to the fuel cell. The air compressor is connected to the oxidant gas supply piping and is rotatable around a rotational shaft. The turbine is connected to the oxidant gas discharge piping and is rotatable around the rotational shaft. The pressure regulating valve is disposed in the oxidant gas discharge piping between the fuel cell and the turbine. The check valve is connected to the oxidant gas discharge piping between the turbine and the pressure regulating valve.