An investigation was carried out to explain the vibrations on an outer ring of a tapered roller bearing. In this report, rigid-body natural vibrations of the outer ring were studied. The tapered roller bearings were operated at a constant speed under an axial load. Axial vibrations of 17 points on the outer ring were detected by two accelerometers. Upon analysis of the axial vibrations, the mode shapes of the rigid-body natural vibrations of the outer ring were obtained. From the experimental results, analyses and considerations, the existence of the rigid-body natural vibrations of the outer ring was proven, and frequency expressions for the rigid-body natural vibrations of the outer ring were derived. Moreover, considerable accuracy of the frequency expressions was shown.