PURPOSE: To enhance the performance of a compressor of axial flow type, by providing a cascade of guide blades, of which height is more than 10% of the width of a passage, of which blade inlet angle is determined such that it can unify the flow in the direction of the width, and of which outlet angle of the final cascade is 0°, to the surface of a wall of the captioned diffuser.

CONSTITUTION: The value such that the blade height is more than 10% of the width of a passage and the blade inlet angle is such that a main stream and a boundary layer can be mixed, kinetic energy of the main stream can be given to the boundary layer, and the flow can be unified to the direction of a width, preferably 0°W45°, is determined on the surface of a wall 3 of the captioned diffuser 1. To the position determined, the cascade of guide blades 6, of which blade outlet angle for the final cascade is 0°, is provided. When a blade inlet angle is determined to 0°W45°, growth of boundary layer is prevented, or the flow is prevented from break-away, in case that the radius of curvature R of a passage is especially small one. In this case, the loss caused by casing 4 is decreased, too, because the speed of a flow at the outlet of a diffuser 1 is decreased, as well as the loss caused by break-away of a diffuser 1 is decreased.