A fuel cell system equipped with a fuel cell that receives the supplies of an anode gas and a cathode gas and generates power comprises: a water content calculation unit for calculating the water content of the fuel cell; an internal impedance calculation unit for calculating the internal impedance of the fuel cell; and a starting time temperature calculation unit for, based on the water content of the fuel cell at the last time when the system was stopped and the internal impedance of the fuel cell at a time when the system is started, calculating the fuel cell temperature at the time when the system is started.