A compressor diffuser is disposed between cylindrical combustion chambers that are disposed around a rotational shaft to supply combustion gas to a turbine and a compressor that is rotatable about the rotational shaft to generate compressed air. The compressor diffuser includes one end connected to an outlet of the compressor; and another end connected to an air inlet of one of the combustion chambers. The one end defines an opening and has double arc portions curving about the rotational shaft, and the other end defines an opening shaped in conformance with the cylindrical shape of the one of the combustion chambers. The compressor diffuser is disposed continuously along an extending direction of the rotational shaft from the one end to the other end.