PURPOSE: To improve efficiency in a compressor as well as to reduce the number of items of parts available to the smallest possible extent, by unifyingly making up a radial diffuser vane converting the velocity energy of an air flow into the pressure energy and an air flow rectifier deflecting a rotating flow to an air flow in an axial direction as one body.

CONSTITUTION: A diffuser device 2 is provided with both a disk part 22 whose diameter is larger than the outer diameter of a hub 12 and a diffuser base 21 having a circular wall part 23 extended over in an axial direction toward the side of a combustor holding chamber 9 from its peripheral edge. A lot of radial diffuser vanes 24 are formed up on the flank of a compressor 1 side of a diffuser base part 22 and air flow rectifiers 25 are as well formed up on the outer surface of the circular wall part 23 of the diffuser base on the other hand, respectively. With this, efficiency in the compressor 1 can be improved and the number of assembling processes is well reduced without any increase of the number of items of parts available.