A fuel cell system includes: a fuel cell stack of fuel cells that generate electricity by electrochemical reaction between hydrogen that is a fuel gas and oxygen that is an oxidant gas; an expander that is provided on a supply path of the fuel gas to the fuel cell stack, and at which, due to the fuel gas that is in a high-pressure state being supplied thereto, the fuel gas is expanded and the pressure thereof is reduced, and, due to the fuel gas being expanded and the pressure thereof being reduced, internal energy of the fuel gas is converted into mechanical energy; and a heating device that is provided further toward an upstream side of the supply path than the expander, and that heats the fuel gas.