A fuel cell system that is compact and has stabilized performance is provided. The fuel cell system includes two fuel cell stacks or a first fuel cell stack (31) and a second fuel cell stack (32), a high-pressure hydrogen tank (11) as a hydrogen supplying device for supplying hydrogen to the first and second fuel cell stacks (31, 32), a compressor (12) as an air supplying device for supplying air to the fuel cell stack, and a humidifier (20) for humidifying air to be supplied to the first and second fuel cell stacks (31, 32). The humidifier (20) is disposed between the first and second fuel cell stacks (31, 32); a supply air exhaust port of the humidifier (20) and air supply ports (Q1) of the first and second fuel cell stacks (31, 32) are connected by air supply pipes (51) having the same length.