PURPOSE: To simplify the structure of a gas turbine engine and to shorten manufacturing procedure by supplying compressed air to the air injection valve and into combustion chamber through air passages formed by casting on the engine casing and on combustor casing in one body respectively.

CONSTITUTION: An air passage 21 is formed on the main casing 1 of the gas- turbine engine in one body as cast, while an air passage 22 is formed on the combustor casing 2 also in one body as cast and both the air passages 21, 22 can be directly connected at respective ends 21A, 22A when assembled. On the other hand, the passage 21 is connected to the outlet 10 of the diffuser and the passage 22 is to an annular path 26. This construction allows compressed air discharged from the compressor to inject into the combustion chamber 24 through the air injection valve 3 via the diffuser 9, its outlet 10, air passages 21, 22 and the annular path 26. Such a construction permis simplification of structure and shortening of manufacturing procedure because the air piping and fittings can be eliminated.