A gas turbine (21;41;61;81;101;121;141) comprising: a compressor section for compressing combustion air; a combustor section for injecting a fuel into high pressure air being sent from the compressor section, to effect combustion so as to generate a high temperature combustion gas; a turbine section which is located at the downstream side of the combustor section, and is arranged to be driven by the combustion gas coming out from said combustor section; a gas turbine casing which houses said compressor section, said combustor section, and said turbine section therein; a stator cooling air system (5;92) for leading compressed air that has been extracted from midstream of said compressor section into stator vanes which are a constituent of said turbine section; and an air bleeding system (6;93) for extracting compressed air from the exit of said compressor section to the outside of said gas turbine casing, wherein midstream of said stator cooling air system (5;92) and midstream of said air bleeding system (6;93) are connected via a connecting path (12;96;132,134), and at midstream of the connecting path (12;96;132,134) there is a flow rate control part (13;97;133,135) connected, wherein a backflow prevention part (23;103;142) is connected to said stator cooling air system (5;92) at the upstream side of a merge point (22;42;102;122;136) where the downstream end of said connecting path (12;96;132,134) is merging, and wherein a turn down operation of the gas turbine is enabled in that the flow rate control part (13;97;133,135) is opened by means of a controller so that the compressed air that has been extracted from the exit of said compressor section flows through said stator cooling air system (5; 92). a compressor section for compressing combustion air; a combustor section for injecting a fuel into high pressure air being sent from the compressor section, to effect combustion so as to generate a high temperature combustion gas; a turbine section which is located at the downstream side of the combustor section, and is arranged to be driven by the combustion gas coming out from said combustor section; a gas turbine casing which houses said compressor section, said combustor section, and said turbine section therein; a stator cooling air system (5;92) for leading compressed air that has been extracted from midstream of said compressor section into stator vanes which are a constituent of said turbine section; and an air bleeding system (6;93) for extracting compressed air from the exit of said compressor section to the outside of said gas turbine casing, wherein midstream of said stator cooling air system (5;92) and midstream of said air bleeding system (6;93) are connected via a connecting path (12;96;132,134), and at midstream of the connecting path (12;96;132,134) there is a flow rate control part (13;97;133,135) connected, wherein a backflow prevention part (23;103;142) is connected to said stator cooling air system (5;92) at the upstream side of a merge point (22;42;102;122;136) where the downstream end of said connecting path (12;96;132,134) is merging, and wherein a turn down operation of the gas turbine is enabled in that the flow rate control part (13;97;133,135) is opened by means of a controller so that the compressed air that has been extracted from the exit of said compressor section flows through said stator cooling air system (5; 92).