Abstract: At a starting of a motor which receives an electric power from a generator driven by an engine, an excitation current controller controls an excitation current so as to cause an output frequency of a generator to approach a predetermined frequency which is lower than a rated frequency when an output voltage detected by an output voltage detector is reduced to lower than a first predetermined voltage. Thereafter, the excitation current controller controls the excitation current so as to cause the output voltage of the generator to be the rated voltage when the output voltage detector detects a second predetermined voltage which is higher than the first predetermined voltage. In this way, the load capacity which enables the starting by the engine-driven generator without directly controlling the engine is improved.