A pre-swirler for a compressor of a gas turbine, comprising: a plurality of first main vanes spaced apart from each other at a predetermined interval along a circumferential direction of a pre-swirler housing , wherein a spacing distance between trailing edges of adjacent first main vanes is L; and a plurality of first auxiliary vanes disposed between the plurality of first main vanes spaced apart from each other and having a size smaller than that of the plurality of first main vanes , wherein a first auxiliary vane of the plurality of first auxiliary vanes is positioned between each pair of adjacent first main vanes and wherein trailing edges of the first main vanes and the first auxiliary vanes are at same axial plane; wherein each first main vane of the plurality of first main vanes includes a first chord length (A) which is a shortest length connecting from a leading edge formed at a tip end portion of a vane body to a trailing edge formed at a rear end portion of the vane body , an intake surface rounded outwardly at a first surface of the vane body , a pressure surface rounded inwardly at a second surface of the vane body opposite the first surface, a first axial chord (B) being the axial length between the leading edge and the trailing edge , and a first stagger angle (D) formed between the first chord length (A) and the first axial chord (B), characterised in that , for each first auxiliary vane positioned between the pair of adjacent first main vanes , a trailing edge of the first auxiliary vane is positioned between adjacent first main vanes at a position of 3L/5 from the trailing edge of the first main vane facing a pressure surface of the first auxiliary vane . a plurality of first main vanes spaced apart from each other at a predetermined interval along a circumferential direction of a pre-swirler housing , wherein a spacing distance between trailing edges of adjacent first main vanes is L; and a plurality of first auxiliary vanes disposed between the plurality of first main vanes spaced apart from each other and having a size smaller than that of the plurality of first main vanes , wherein a first auxiliary vane of the plurality of first auxiliary vanes is positioned between each pair of adjacent first main vanes and wherein trailing edges of the first main vanes and the first auxiliary vanes are at same axial plane; wherein each first main vane of the plurality of first main vanes includes a first chord length (A) which is a shortest length connecting from a leading edge formed at a tip end portion of a vane body to a trailing edge formed at a rear end portion of the vane body , an intake surface rounded outwardly at a first surface of the vane body , a pressure surface rounded inwardly at a second surface of the vane body opposite the first surface, a first axial chord (B) being the axial length between the leading edge and the trailing edge , and a first stagger angle (D) formed between the first chord length (A) and the first axial chord (B), characterised in that , for each first auxiliary vane positioned between the pair of adjacent first main vanes , a trailing edge of the first auxiliary vane is positioned between adjacent first main vanes at a position of 3L/5 from the trailing edge of the first main vane facing a pressure surface of the first auxiliary vane . <EOS>