a pilot nozzle provided on a center axis of said combustor, wherein the pilot nozzle performs diffusion combustion;

a plurality of main nozzles equally spaced apart from each other and provided around an outside circumference of the pilot nozzle, wherein the plurality of nozzles perform premixed combustion;

a combustor basket covering the outside circumferences of the pilot nozzle and the plurality of main nozzles;

a cylinder connected to an end of the combustor basket adjacent to a bases of each of the main nozzles, wherein the cylinder includes an outside wall curved upward in a direction from the tips of each of the main nozzles to the bases of each of the main nozzles wherein a cross-section of the outside wall adjacent to the bases of the main nozzle has a semicircular configuration;

an external cylinder provided around an outside circumferences of the combustor basket and the cylinder wherein a space between an inside wall of the external cylinder and an outside wall of the combustor basket or the cylinder functions as a passageway for compressed air;

a back surface wall that covers the inner side of the external cylinder around the bases of the main nozzles of the external cylinder, the back surface wall having a surface curved toward the inside wall of the external cylinder where a back surface is formed into a bowl shape with respect to the position of the bases of the main nozzles; and

a turning vane formed of a one-piece material and having a substantially arc-shape is provided between each of the main nozzles that are circumferentially adjacent to each other,

wherein the turning vane curves from the outside circumference of the main nozzle towards a central axis of the main nozzle, when viewed from a direction upstream of the cylinder, and connects the side surfaces of each of the adjacent main nozzles.