A radial non-contact lip (26) having a tip edge that is positioned further radially inward than is the inner peripheral surface at an axial end of an inner ring (7) is formed on the inner peripheral edge of a seal ring (20) that axially faces a flange part (18a) constituting a bearing holder (3a), the seal ring (20) being one of a pair of seal rings (20, 9b) that block the openings at the two axial ends of a release bearing (2a). A labyrinth seal (30) is formed, between the axial-side surface of the radial non-contact lip (26) and the axial end surface of the inner ring (7), radially inward from a sliding contact part (40) between the tip edge of a contact lip (12a) and the axial inner end surface of the inner ring (7).