To solve the problem of deterioration of the efficiency of power generation, which occurs if a generator is operated by power source equipment whose speed changes by its operating conditions, as windmill power generating facilities of a fixed-blade propeller.

Against a motive power change, power source equipment 1 is operated in the vicinity of its optimum rotational speed, a generated voltage by a generator 2 is increased up to a constant voltage by a booster circuit 3, and this output is converted into a constant frequency by a frequency converter 4 and is outputted. The booster circuit is composed of a transformer with taps, a rectifier and a boosting chopper. Besides, the booster circuit is fitted with a switch for by-passing the boosting chopper, or the rectifier, and the boosting chopper and the frequency converter, when boosting is unnecessary. Besides, the booster circuit utilizes the inductances of the windings of the generator, and has DC chopper configuration.