A fuel cell system which prevents the deterioration of the fuel cell stack when feeding of the oxidant gas is paused under a load to perform a fuel conservation operation. Controller shuts down oxidant gas compressor and cooling water circulating pump to execute fuel conservation operation at a low fuel cell system load. The controller gives a current draw instruction to electric power controller. In the fuel conservation operation, electric power controller draws a current larger than zero from fuel cell stack, and keeps the total charge drawn per unit time constant or substantially constant.