Abstract: A generating system having a rotating type generator to interconnect a power system in order to output power of the generator to the power system comprises a generator, an exciting circuit and an excitation control section. It also comprises short-cycle stabilizing sections for outputting a short-cycle stabilizing signal for suppressing short-cycle power fluctuations according to at least one of an electric parameter and a mechanical parameter of the generator and a long-cycle stabilizing section for outputting a long-cycle stabilizing signal for suppressing long-cycle power fluctuations having a cycle time longer than short-cycle power fluctuations according to the mechanical parameter of the generator. The outputs of the short-cycle stabilizing sections and the long-cycle stabilizing section are sent to the excitation control section.