A seal lip portion 9 includes a lip main body (9a) and a projecting section (16) protruding from a peripheral edge of the lip main body (9a) and slidingly engageable with an inner ring (1), and this projecting section (16) is made of a highly frictionally wearable material which allows the projecting section (16), when frictionally worn, to establish a non-contact or a light contact to such an extend as to result in a contact pressure that can be regarded as zero. A fitting section (13) fitted into a seal mounting groove (2b) in a seal member main body (8) is held in a drag-rotation preventive structure that prevents circumferential movement due to a drag-rotation relative to an outer ring (2).