The gas turbine engine (S1) includes: turbine blades (7b); and a cooling air supply unit (11) to supply cooling air to the turbine blades (7b). A flow path surface (31) is formed so as to be positioned in an upstream side of the turbine blades (7b) and so as to be connected to a base surface (32) in which the turbine blades (7b) are provided. The flow path surface (31) includes: depression portions (31a) depressed relative to the base surface (32), each depression portion (31a) including at least an area overlapping with a front end (7b1) of each turbine blade (7b), when viewed from a direction of the turbine axis (L); and protrusion portions (31b) protruding relative to the base surface (32), each protrusion portion (31b) being at least part of each area positioned between front ends (7b1) of the turbine blades (7b), when viewed from the above direction.