A brush seal assembly (1) includes a brush seal (10), a brush support portion (20), and an assembly support portion (30). The brush seal, which has a multitude of bristles forming an angle with respect to a radial direction of a rotating body (2) rotated inside a casing, is disposed around an outer circumferential surface of the rotating body and is oriented with respect to the body's rotating direction. The brush support portion supports the brush seal by extending toward the rotating body while contacting a low-pressure side of the brush seal. The assembly support portion supports 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.