A bearing unit A comprises a main shaft gear 1 integrally having a tooth section 1a always meshed with a sub shaft gear 6 at the outer circumference, a pair of inner rings 2 fitted in the outer circumference of the main shaft 5, double-row tapered rollers 3 disposed between the raceway surface of the main shaft gear 1 and that of the inner ring 2, and a pair of cages 4 for respectively retaining each row of tapered rollers 3. The pockets 4a of the cage 4 are unequally pitched, wherein the tapered rollers 3 housed in the pockets 4a are unequally disposed at the circumference.