A fuel cell system includes a fuel cell that includes an anode and a cathode and generates electricity by reducing a mediator at the cathode, a regenerator that oxidizes the mediator, a fuel gas feed path through which fuel gas to be supplied to the anode flows, a humidifier that is disposed in the fuel gas feed path and humidifies the fuel gas, and a water collection path that extends from the regenerator to the humidifier and guides to the humidifier at least one selected from steam produced at the regenerator and condensation formed from the steam.