A sealing device includes an annular seal portion formed of an elastic material. On an inner peripheral surface of the seal portion, a main lip is formed so as to be in slidable contact with an outer peripheral surface of a rotary shaft, and a vacuum space side inclined surface is formed so as to gradually enlarge in diameter from the main lip toward a vacuum space side. On the vacuum space side inclined surface, a plurality of annular projections are formed along an axial direction so as to be in slidable contact with the outer peripheral surface of the rotary shaft in a state where the main lip is in slidable contact with the outer peripheral surface of the rotary shaft.