To provide a fuel cell system capable of preventing reverse flow of water to a tank used for circulation of water inside the fuel cell system and enhancing the degree of freedom of a layout of the tank in the fuel cell system.

The fuel cell system is equipped with an anode side gas-water separation tank 10 for separating water from anode offgas in a fuel cell stack 3, a cathode side gas-water separation tank 20 for separating water from cathode offgas of the fuel cell stack 3, a supply pipe 21 for supplying water in the cathode side gas-water separation tank 20 to the fuel cell stack 3, and a communication pipe 11 for supplying water in the anode side gas-water separation tank 10 to the supply pipe 21, and pumps 22a, 23a are installed in the supply pipe 21, and the communication pipe 11 is communicated with the supply pipe 21 on the suction sides of the pumps 22a, 23a.