A fuel cell system (S) is provided with a fuel cell body (12), an air supply system (1, 2, 3, 4) supplying air to the fuel cell body, an air flow rate control system (5, 6, 7, 8, 9, 10, 13, 14) varying opening degrees of flow paths, through which air is supplied, to control flow rates of air, and a droplet removal structure (3, 8, 9, 10, 13, 14, 19, 20, 21, 22, 23, 24) removing droplets adhered to the air flow rate control system. The droplet removal structure is operative to set the opening degree of the air flow rate control system to have a droplet removal opening degree to increase a speed with which the air flows and allows the air to flow at the droplet removal opening degree for blowing off the droplets adhered to the air flow rate control systems.