METHOD OF OPERATING FUEL CELL SYSTEM

A fuel cell system includes a fuel cell stack, a fuel gas supply channel, a fuel gas circulation channel, a circulating pump that is driven by a pump motor having no sensor, and an ECU for controlling the rotation of the pump motor. A method for operating the fuel cell system rotates the pump motor when starting, and stops the supply of electric power to the pump motor after the rotational speed of the pump motor has reached a given value, and determines, in an inertial period, whether or not the rotational speed of the pump motor has become equal to or lower than a predetermined value within a given time period.