A brush seal assembly for a gas turbine, comprising: a brush seal disposed around an outer circumferential surface of a rotating body rotated inside a casing and oriented with respect to a rotating direction of the rotating body, the brush seal having a multitude of bristles forming an angle with respect to a radial direction of the rotating body; a brush support portion configured to support the brush seal by extending toward the rotating body while contacting a low-pressure side of the brush seal, wherein the low-pressure side of the brush seal is an axially rear side of the brush seal; and an assembly support portion configured to support the brush seal and the brush support portion and to receive respectively a base end of the brush seal and an axial protrusion of the brush support portion, wherein the assembly support portion includes: a first support; a second support configured to support the brush support portion from an axially rear side of the brush support portion opposite to the contact with the brush seal; and a third support disposed between the first and second supports (32, 34) to jointly support the brush seal and the brush support portion; characterized in that the brush seal assembly further comprises a first fluid space formed between the brush seal and the first support facing the brush seal, and wherein the brush support portion comprises a plurality of inclined plates respectively extending toward the rotating body, and a second fluid space is formed between the brush support portion and the second support facing the brush support portion. a brush seal disposed around an outer circumferential surface of a rotating body rotated inside a casing and oriented with respect to a rotating direction of the rotating body, the brush seal having a multitude of bristles forming an angle with respect to a radial direction of the rotating body; a brush support portion configured to support the brush seal by extending toward the rotating body while contacting a low-pressure side of the brush seal, wherein the low-pressure side of the brush seal is an axially rear side of the brush seal; and an assembly support portion configured to support the brush seal and the brush support portion and to receive respectively a base end of the brush seal and an axial protrusion of the brush support portion, wherein the assembly support portion includes: a first support; a second support configured to support the brush support portion from an axially rear side of the brush support portion opposite to the contact with the brush seal; and a third support disposed between the first and second supports (32, 34) to jointly support the brush seal and the brush support portion; characterized in that the brush seal assembly further comprises a first fluid space formed between the brush seal and the first support facing the brush seal, and wherein the brush support portion comprises a plurality of inclined plates respectively extending toward the rotating body, and a second fluid space is formed between the brush support portion and the second support facing the brush support portion. a first support; a second support configured to support the brush support portion from an axially rear side of the brush support portion opposite to the contact with the brush seal; and a third support disposed between the first and second supports (32, 34) to jointly support the brush seal and the brush support portion; the brush seal assembly further comprises a first fluid space formed between the brush seal and the first support facing the brush seal, and wherein the brush support portion comprises a plurality of inclined plates respectively extending toward the rotating body, and a second fluid space is formed between the brush support portion and the second support facing the brush support portion.