A control device 7 obtains a reformed carbon quantity C supplied to a reform reaction flow channel 21 from a supplied fuel quantity Qf and also obtains a reformed water quantity S supplied to the reform reaction flow channel 21 from a generated power quantity W. Further, it obtains a oxygen consumed quantity consumed through power generation in a fuel cell 3 from the generated power quantity W, a supplied oxygen quantity to be supplied to a cathode flow channel 33 from a supplied cathode gas quantity Qc, and a reformed oxygen quantity O to be supplied to the reform reaction flow channel 21 based on a difference between the supplied oxygen quantity and the consumed oxygen quantity. By correcting a reformed carbon quantity C (delivery of a fuel pump 51) in accordance with the reformed oxygen quantity O, each of O/C and S/C is kept in a target value range.