A sealing device which includes an annular exterior sealing member; a reinforcing ring disposed in a housing hole to surround an outer circumference of a rotating shaft and to press a fitting portion of the exterior sealing member against an inner circumference surface of the housing hole; a retainer mounted in the reinforcing ring; an auxiliary sealing member having one end portion that is pinched and retained between the retainer and the reinforcing ring and the other end portion that is pressed against the outer circumference surface of the rotating shaft; and an elastic tongue piece and an engagement portion that are provided between the retainer and the reinforcing ring.