To easily and certainly attach a seal member to a peripheral groove on the inner ring side without reducing sealing performance.

This bearing unit comprises an outer ring 3, a rolling element 5, an inner ring 4, the peripheral groove 6 formed in the inner ring 4 axially outside an inner ring track surface 4a or the outer periphery of a member integrated with the inner ring, and a seal member 7 to be attached by engagement with the peripheral groove 6. A projecting part 11 in contact with the inner wall surface of the peripheral groove 6 by pressure is formed over the whole circumference of the seal member 7 on a side surface of an engagement base 9 of the seal member 7, and a receiving recessed part 12 for receiving the compressed and deformed projecting part 11 is formed on the outer diameter side of the projecting part 11. In engagement of the engagement base 9 into the peripheral groove 6, the projecting part 11 deforms so as to be folded into the outer diameter side and comes into the recessed part 12 lying on the outer diameter side.