A fuel cell system comprising: a fuel cell that generates power using a fuel gas and an oxidizing gas; a first supply flow path through which the fuel gas to be supplied to an anode of the fuel cell flows; a second supply flow path through which the oxidizing gas to be supplied to a cathode of the fuel cell flows; a recycle flow path which is connected between the anode and the first supply flow path and through which an anode off gas discharged from the anode flows; a circulator that is provided in the recycle flow path and that allows the anode off gas to flow into the first supply flow path; a discharge flow path which branches off from the recycle flow path and through which the anode off gas flows; a reservoir that is provided in the discharge flow path and that stores water condensed from the anode off gas; a valve provided in the discharge flow path downstream of the reservoir; and a controller, characterized in that the controller, in a purge operation: opens the valve, determines a pressure in the discharge flow path based on an amount of the water stored in the reservoir and a discharge time of the water that flows through the discharge flow path to be discharged, and determines an open time, for which the valve is opened to discharge the anode off gas, based on the pressure in the discharge flow path and a discharge amount of the anode off gas that flows through the discharge flow path to be discharged, and closes the valve when an elapsed time for which the valve is opened reaches the open time. a fuel cell that generates power using a fuel gas and an oxidizing gas; a first supply flow path through which the fuel gas to be supplied to an anode of the fuel cell flows; a second supply flow path through which the oxidizing gas to be supplied to a cathode of the fuel cell flows; a recycle flow path which is connected between the anode and the first supply flow path and through which an anode off gas discharged from the anode flows; a circulator that is provided in the recycle flow path and that allows the anode off gas to flow into the first supply flow path; a discharge flow path which branches off from the recycle flow path and through which the anode off gas flows; a reservoir that is provided in the discharge flow path and that stores water condensed from the anode off gas; a valve provided in the discharge flow path downstream of the reservoir; and a controller, characterized in that the controller, in a purge operation: opens the valve, determines a pressure in the discharge flow path based on an amount of the water stored in the reservoir and a discharge time of the water that flows through the discharge flow path to be discharged, and determines an open time, for which the valve is opened to discharge the anode off gas, based on the pressure in the discharge flow path and a discharge amount of the anode off gas that flows through the discharge flow path to be discharged, and closes the valve when an elapsed time for which the valve is opened reaches the open time. opens the valve, determines a pressure in the discharge flow path based on an amount of the water stored in the reservoir and a discharge time of the water that flows through the discharge flow path to be discharged, and determines an open time, for which the valve is opened to discharge the anode off gas, based on the pressure in the discharge flow path and a discharge amount of the anode off gas that flows through the discharge flow path to be discharged, and closes the valve when an elapsed time for which the valve is opened reaches the open time.