A combustion turbine power generating system includes an AC power generator, a combustion turbine that drives the AC power generator, a first converter that can make conversion between AC current and DC current and having an AC side connected to the AC power generator, a second converter that can make conversion between AC current and DC current and having a DC side connected to a DC output side of the first converter, a smoothing condenser connected between the first and second converters, a generator-speed control unit that controls the first converter and a DC voltage control unit that controls a DC-side voltage of the second converter, thereby the generator-speed control unit controls the first converter on the basis of the number of revolution command value.