A fuel cell system includes a fuel cell stack, a heat exchanger, an evaporator, a reformer, and a combustor. A fluid unit including at least the heat exchanger, the evaporator, and the reformer is provided at one end of the fuel cell stack in a stacking direction. The combustor is provided inside the evaporator. The combustor has a combustion gas path for discharging a combustion gas produced in the combustor. The reformer is provided at a position in the middle of the combustion gas path.