A brush seal device (100, 200, 500) having a brush seal (110, 210), a back plate part and a holding part, and sealing in an axial direction between a housing and a rotational shaft, said brush seal (110, 210) comprises: an inner circumferential brush seal (120, 220), an outer circumferential brush seal (140, 240, 540), and a connection part (112, 212, 503) where an outer circumferential side of the inner circumferential brush seal (120, 220) and an inner circumferential side of the outer circumferential brush seal (140, 240, 540) are joining; wherein said inner circumferential brush seal (120, 220) comprises; an inner-circumferential-side brush portion in which a plurality of bristles (121, 211) are arranged from the connection part (112, 212, 503) to an inner circumferential direction, and an inner-circumferential-side free end portion which is an inner-circumferential-side end portion of the inner-circumferential-side brush portion and is arranged opposite to an outer circumferential surface of the rotational shaft so as in use to contact or be adjacent to the outer circumferential surface, said outer circumferential brush seal (140, 240, 540) comprises; an outer-circumferential-side brush portion (143, 543) in which a plurality of bristles (141, 211, 541) are arranged from the connection part (112, 212, 503) to an outer circumferential direction, and an outer-circumferential-side free end portion (145, 545) which is an outer-circumferential-side end portion of the outer-circumferential-side brush portion (143, 543) and is arranged opposite to an inner circumferential surface of the housing so as in use to contact or be adjacent to the inner circumferential surface, characterised in that said back plate part is an annular plate member placed at the lower pressure side of the brush seal (110, 210), the back plate part being placed so that a side surface thereof is contacted to the bristles (121, 211) of the inner circumferential brush seal (120, 220), the back plate part supporting the bristles (121, 211), which receives pressure of process fluid, from the lower pressure side, an opening, which makes the rotational shaft go through, being formed on the central position of the back plate part, said holding part is an annular plate member placed at the higher pressure side of the brush seal (110, 210), the holding part being placed so that a side surface thereof is contacted to the bristles (121, 211) of the inner circumferential brush seal (120, 220), an opening, which makes the rotational shaft go through, being formed on the central position of the holding part, and the opening of the holding part have a diameter which is larger than a diameter of the opening of the back plate part. an inner circumferential brush seal (120, 220), an outer circumferential brush seal (140, 240, 540), and a connection part (112, 212, 503) where an outer circumferential side of the inner circumferential brush seal (120, 220) and an inner circumferential side of the outer circumferential brush seal (140, 240, 540) are joining; wherein said inner circumferential brush seal (120, 220) comprises; an inner-circumferential-side brush portion in which a plurality of bristles (121, 211) are arranged from the connection part (112, 212, 503) to an inner circumferential direction, and an inner-circumferential-side free end portion which is an inner-circumferential-side end portion of the inner-circumferential-side brush portion and is arranged opposite to an outer circumferential surface of the rotational shaft so as in use to contact or be adjacent to the outer circumferential surface, said outer circumferential brush seal (140, 240, 540) comprises; an outer-circumferential-side brush portion (143, 543) in which a plurality of bristles (141, 211, 541) are arranged from the connection part (112, 212, 503) to an outer circumferential direction, and an outer-circumferential-side free end portion (145, 545) which is an outer-circumferential-side end portion of the outer-circumferential-side brush portion (143, 543) and is arranged opposite to an inner circumferential surface of the housing so as in use to contact or be adjacent to the inner circumferential surface, characterised in that said back plate part is an annular plate member placed at the lower pressure side of the brush seal (110, 210), the back plate part being placed so that a side surface thereof is contacted to the bristles (121, 211) of the inner circumferential brush seal (120, 220), the back plate part supporting the bristles (121, 211), which receives pressure of process fluid, from the lower pressure side, an opening, which makes the rotational shaft go through, being formed on the central position of the back plate part, said holding part is an annular plate member placed at the higher pressure side of the brush seal (110, 210), the holding part being placed so that a side surface thereof is contacted to the bristles (121, 211) of the inner circumferential brush seal (120, 220), an opening, which makes the rotational shaft go through, being formed on the central position of the holding part, and the opening of the holding part have a diameter which is larger than a diameter of the opening of the back plate part.