An aircraft gas turbine is constituted by accommodating a compressor (14), a combustor (15), and a turbine (16) in a cylindrical main unit casing (12). A thick wall part (52) is provided on an outer periphery side of rotor blades (34) in the main unit casing. A cooling passage (53), for cooling the thick wall part (52) by circulating compressed air compressed by the compressor, is provided in the thick wall part. Also provided is a discharge passage (55) for discharging compressed air having circulated in the cooling passage to a combustion gas passage A. The structural strength of the thick wall part is ensured by appropriately cooling the thick wall part of the casing, while simplifying the structure and preventing a decrease in efficiency, thereby ensuring effective containment performance and an appropriate clearance between the casing and the rotor blades.