PURPOSE: To reduce the generation of nitrogen oxide in a combustion apparatus for a gas turbine used in a thermal power plant or the like, by providing a contraction annular member between two flame tubes thereby to contract a gas flowing thereinto.

CONSTITUTION: An injection nozzle 3 for supplying a fuel and a swirler 4 for controlling a combustion air are concentrically provided on the upper part 1a of a first flame tube 1. The first flame tube 1 is further provided in its lower part 1b with a contraction annular member 5 with an incombustible-gas supply pipe 5a. An annular hollow 8 is formed between inner and outer tubes 7, 6 constituting the contraction annular member 5 so that the gas flowing thereinto from the incombustible-gas supply pipe 5a is swirled. In addition, the inner tube 7 is provided in its peripheral wall with nozzles 9, 10 which increase in size from the upstream side toward the downstream side. Thus, the swirled incombustible- gas flows into a combustion flow path 11 while being properly reduced in pressure, and well burns in a second combustion chamber 12 to produce a high- temperature high-pressure gas, so that a cooling air and the fuel is mixed at an equivalent ratio. Thus, the generation of nitrogen oxide is reduced.