Provided is a fuel cell system that can effectively suppress clogging of a pipe due to freezing of water in a fuel gas supply system thereof without the need for halting the operation of the fuel cells, and thus is highly reliable. When possible freezing of water is detected or presumed to be present downstream of an injector, the amount of a fuel gas to be supplied from a circulation pump that is disposed in a circulation channel is relatively increased compared to the amount of the fuel gas to be supplied from the injector.