A fuel cell system according to one embodiment of the present invention comprises: a fuel treatment device which supplies fuel gas containing hydrogen; an oxidant gas supply device which supplies oxidant gas containing oxygen; a fuel cell stack which initiates an electrochemical reaction using the fuel gas and the oxidant gas; a cooling device which cools heat generated by the fuel cell stack; a heat recovery device which recovers waste heat from the high temperature cooling water supplied by the cooling device, circulated through the fuel cell stack, and discharged; and a vapor-generating device which supplies water with a pressure to generate vapor using the waste heat from the fuel treatment device, and which supplies the thus-generated vapor to at least the fuel gas or the oxidant gas being supplied to the fuel cell stack to humidify the fuel gas or the oxidant gas.
