A fuel cell system includes: a fuel cell (11) which generates electric power by using a fuel gas and an oxidizing gas; an anode off-gas channel for flow of an anode off gas discharged from an anode (2a) of the fuel cell (11); a gas/liquid separator (10) which is arranged in the anode off-gas channel (34) for separating moisture from the anode off-gas and has a water reservoir (18) for containing the separated moisture as water; a temperature detector (28) which detects the temperature of the reservoir (18); and an operation permitting unit (52) which is configured not to permit operation of the fuel cell system if the detection temperature obtained by the temperature detector (28) exceeds a first threshold value which is higher than the standard environment temperature.
