To provide a sealing device of a rolling bearing which maintains sealing performance under severe conditions, and sufficient water-proof and dust-proof performances.

In this sealing device 2, a waist part 11 of a lip part 7 is almost perpendicular to a rotation center shaft J in the state where fitted to an outer ring 3 and an inner ring 6. Thus, even if a centrifugal force when the outer ring 3 is rotated acts on the waist part 11 of the lip 7, a force to bend this waist part 11 in the axial direction is rarely generated. Also, in this sealing device 2, in the free state where not fitted to an outer ring 1 or to the inner ring 6, the waist part 11 of the lip part 7 is inclined inwardly in the axial direction by an inclination angle of 10 degrees to a reference level S crossing the rotation center shaft J. By this, a tensile force of the lip part 7 against the inner ring 6 is set at an optimum value at fitting, and sealing performance is maintained even under the severe conditions.