The present invention is a fuel cell system comprising: a hydrogen generator including a reformer which has a reforming catalyst and carries out a reforming reaction using the reforming catalyst to generate a hydrogen-containing gas from a raw material, a shift converter which has a shift catalyst and carries out a shift reaction using the shift catalyst to decrease carbon monoxide in the hydrogen-containing gas, and a first temperature detector which detects a temperature of the shift converter; a fuel cell which uses the hydrogen-containing gas delivered from the hydrogen generator, to generate electric power; and a control unit, wherein: the control unit does not start delivering the hydrogen-containing gas from the hydrogen generator to the fuel cell when at least the temperature of the shift converter detected by the first temperature detector is not a stable determination temperature or higher; and the stable determination temperature is lower than a control temperature of the shift converter at the time of a normal operation.