A fuel cell system includes: a fuel cell to generate electric power; a casing accommodating at least the fuel cell, the casing including an air inlet and an exhaust outlet; a supply passage connected to the air inlet, to introduce external air into the casing; an exhaust passage connected to the exhaust outlet, to exchange heat with the supply passage and discharge at least air inside the casing; an air supply device to introduce the external air into the casing; a temperature detector to detect a temperature; and a controller configured to control at least the air supply device. If the temperature detected by the temperature detector after the controller has caused the air supply device to operate is lower than or equal to a first predetermined temperature, the controller reduces an amount of air supplied by the air supply device and causes the air supply device to continue operating.