The raceway groove width (W) of the inner ring 2 and the length (L) of the tapered roller 3 are finished within predetermined dimensional tolerances. The retaining rib face 2b of the inner ring 2 is machined such that it is a surface parallel to the small end faces 3b of the tapered rollers 3. The clearances .delta. which are defined when the tapered rollers 3 are disposed on the raceway surface 2a of the inner ring 2 and are contacted at the large end faces 3a thereof with the cone back face rib face 2c is secured to be within the dimensional range, .delta..ltoreq.0.4 mm.