An internal batch mixer, comprising: a mixing device for mixing material; and a display device provided outside said mixing device, wherein said mixing device includes: a casing having a mixing chamber (4a, 4b) inside; a rotor inserted to said mixing chamber; a rotor shaft provided to protrude from a rotor end surface that is an end surface in the axial direction of said rotor; and a dust stop device for arresting leak of the material within said mixing chamber (4a, 4b) to the outside, and said dust stop device includes: a rotation-side seal member fixed to said rotor end surface to be rotated integrally with said rotor; a ring-like fixed-side seal member through which said rotor shaft is rotatably inserted; and a pressing force imparting mechanism which is adapted to bias said fixed-side seal member toward said rotor end surface so that said fixed-side seal member is in pressure contact with said rotation-side seal member, and said pressing force imparting mechanism includes: a linear actuator which has a moving part provided to be movable in the axial direction of said rotor, and adapted to bias said fixed-side seal member toward said rotor end surface by moving said moving part toward said rotor end surface; characterized by a linear sensor attached to said linear actuator to detect displacement of said moving part in the axial direction of said rotor, wherein said display device is adapted to display displacement information of said fixed-side seal member based on a detection value by said linear sensor in a state where said fixed-side seal member is in pressure contact with said rotation-side seal member by said pressing force imparting mechanism. a mixing device for mixing material; and a display device provided outside said mixing device, wherein said mixing device includes: a casing having a mixing chamber (4a, 4b) inside; a rotor inserted to said mixing chamber; a rotor shaft provided to protrude from a rotor end surface that is an end surface in the axial direction of said rotor; and a dust stop device for arresting leak of the material within said mixing chamber (4a, 4b) to the outside, and a casing having a mixing chamber (4a, 4b) inside; a rotor inserted to said mixing chamber; a rotor shaft provided to protrude from a rotor end surface that is an end surface in the axial direction of said rotor; and a dust stop device for arresting leak of the material within said mixing chamber (4a, 4b) to the outside, and said dust stop device includes: a rotation-side seal member fixed to said rotor end surface to be rotated integrally with said rotor; a ring-like fixed-side seal member through which said rotor shaft is rotatably inserted; and a pressing force imparting mechanism which is adapted to bias said fixed-side seal member toward said rotor end surface so that said fixed-side seal member is in pressure contact with said rotation-side seal member, and a rotation-side seal member fixed to said rotor end surface to be rotated integrally with said rotor; a ring-like fixed-side seal member through which said rotor shaft is rotatably inserted; and a pressing force imparting mechanism which is adapted to bias said fixed-side seal member toward said rotor end surface so that said fixed-side seal member is in pressure contact with said rotation-side seal member, and said pressing force imparting mechanism includes: a linear actuator which has a moving part provided to be movable in the axial direction of said rotor, and adapted to bias said fixed-side seal member toward said rotor end surface by moving said moving part toward said rotor end surface; characterized by a linear sensor attached to said linear actuator to detect displacement of said moving part in the axial direction of said rotor, wherein a linear actuator which has a moving part provided to be movable in the axial direction of said rotor, and adapted to bias said fixed-side seal member toward said rotor end surface by moving said moving part toward said rotor end surface; characterized by a linear sensor attached to said linear actuator to detect displacement of said moving part in the axial direction of said rotor, wherein said display device is adapted to display displacement information of said fixed-side seal member based on a detection value by said linear sensor in a state where said fixed-side seal member is in pressure contact with said rotation-side seal member by said pressing force imparting mechanism.