To provide a sealing device capable of achieving excellent sealing performance in severe conditions such as possible exposure to mass quantity of mud water, and achieving long service life.

This sealing device is provided with a side lip (seal lip) 12 fixed in a sealing way to a housing (one member) 1, with a tip slidably and tightly applied to an end surface 22a of a slinger (the other member) 20 installed on a rotation shaft 2. In a back surface 12b of the slide lip 12 to be set back-to-back to the slider 20, a plurality of fins 15 are formed to extend at a prescribed angle to a rotation direction. As liquid flows toward the back surface 12b of the slide lip 12, flow of liquid in accordance with rotation is converted into pressure of the side lip 12 by means of the fins 15. Tight contact surface pressure to the slinger 20 is thus increased, and excellent sealing performance is achieved. In case there is no liquid flowing toward the back surface 12b, tight contact surface pressure of the side lip 12 is small, so that abrasion due to sliding is restricted.

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