The fuel cell system enabling shortening of the startup time of the system and preventing a pressure sensor from malfunctioning is provided. The fuel system 1 includes a fuel cell 10; a hydrogen tank 22 supplying hydrogen gas to the anode side of the fuel cell 10 through a hydrogen supply channel 43; an air pump 21 supplying air to the cathode side of the fuel cell 10 through an air supply channel 41; a bypass 46 connecting the air supply channel 41 with the hydrogen supply channel 43; an air induction valve 461 provided on the bypass 46, enabling control of the amount of gas flowing in the bypass 46; and a pressure sensor 51 having a diaphragm which is deformable by the pressure of the hydrogen gas, the pressure sensor detecting pressure of hydrogen gas by detecting displacement of the diaphragm.