A gas
turbine engine has, in a cross section in the axial direction of an annular inner
peripheral wall connected to a blade main body of a
turbine blade, a concave part and a convex part on the
front edge side and the rear edge side. The concave part has a negative curvature and is concave toward the axis, and the convex part has a positive curvature and is convex away from the axis. The flow rate on the upper face of the blade main body can be reduced in the concave part on the
front edge side, thus suppressing generation of a
shock wave, and the flow rate can be increased in the convex part on the rear edge side following the concave part, thus smoothly changing the flow rate on the upper face of the blade main body and thereby minimizing the pressure loss. In this way, the thickness of the blade main body can be reduced while ensuring the performance of the gas
turbine engine, thereby contributing to a reduction in weight.