Abstract: The present invention provides a fuel cell system including a reformer that reforms a raw fuel using a reforming catalyst to generate reformed gas, a fuel cell that generates electric power using the reformed gas generated by the reformer, a heat exchanger that exchanges heat between heat of combustion exhaust gas discharged from the fuel cell and water introduced thereinto, a condenser that condenses steam contained in the combustion exhaust gas discharged from primary side downstream of the heat exchanger to recover water, a pump for supplying the water to secondary side upstream of the heat exchanger; a hot-water temperature measurement instrument that measures temperature of hot water at secondary side downstream of the heat exchanger, and a control unit that controls a supply amount by the pump.