To reduce the pressure of gas supplied to the first side of a hydrogen separation membrane and achieve miniaturization of a compressor.

In this fuel cell system for a traveling body, anode gas from a fuel cell 10 is circulated to the hydrogen separation membrane 8a while reformed gas is supplied to the hydrogen separation membrane 8a and hydrogen passing through the hydrogen separation membrane 8a is supplied to the fuel cell 10. The hydrogen separation membrane 8a is divided into a first side chamber 81, to which the reformed gas is supplied and a second side chamber 82 from which the hydrogen passing through the hydrogen separation membrane 8a is extracted. A steam generating means 14 for cooling the hydrogen and generating steam by waste heat of the hydrogen is disposed downstream of the second side chamber 82. The steam from the steam generating means 14 is supplied to the second side chamber 82.