FUEL CELL SYSTEM

A fuel cell system (1) includes a controller (50) configured to control opening and closing of a drain valve (28) and opening and closing of an exhaust valve (29). The controller (50) is configured to, when an amount of water stored in a gas-liquid separator (27) is larger than or equal to a predetermined value, open the drain valve (28) to drain, via the drain valve (28), the water stored in the gas-liquid separator (27). The controller (50) is configured to, when a concentration of impurities contained in circulating gas is higher than or equal to a predetermined value, open the exhaust valve (29) to release, via the exhaust valve (29), the circulating gas circulating in the circulating path (23).