PURPOSE: To promote the improvement of efficiency in the time of partial load operation, by throttling a throat of a variable stator blade in a high load region and increasing an area of the throat in partial load region.

CONSTITUTION: Air is compressed by a compressor C, and the air, after it is preheated by a regenerative heat exchanger R, is heated by a combustor B. Combustion gas is supplied to an output turbine PT and a turbine GT which drives the compressor. A variable stator blade VN is provided between both the turbines PT, GT. Pressure ratio of the compressor C is increased by throttling a throat of the variable stator blade in a high load region. The pressure ratio is decreased by increasing an area of the throat in a partial load region, and a heat regenerating rate is increased. In this way, efficiency in the time of partial load operation can be enhanced.