A sealing device comprises a stationary-side installation ring (11) fixed to an outer stationary-side member (201), a rotation-side installation ring (12) fixed to an inner rotation-side member (202), a stationary-side lip (13) provided on the stationary-side installation ring (11) to be slidably in contact with the rotation-side installation ring (12) by its tip, rotation-side lips (14, 15) formed on the rotation-side installation ring (12) to be slidably in contact with the stationary-side installation ring (11) by their tips, a pulsar ring (17) formed of a synthetic resin or rubber-like elastic material mixed with magnetic powder on the rotation-side installation ring (12) and multipolar magnetized, and a collar portion (17a) formed on an outer periphery of the pulsar ring (17) at the outer side than the rotation-side lips (14, 15) to closely face the stationary-side member (201) or the stationary-side installation ring (11), thereby an excellent sealing ability being given.