A rotary apparatus comprises a non-rotary part, a rotary shaft, a rotary member between the rotary shaft and the non-rotary part, an inside bearing between the rotary shaft and the rotary member, and an outside bearing between the rotary member and the non-rotary part. The inside bearing comprises first and second inside bearings spaced along a direction of a central axis of the rotary shaft. The outside bearing comprises first and second outside bearings spaced along the rotary shaft. An outer ring of the first inside bearing and an inner ring of the first outside bearing, and an outer ring of the second inside bearing and an inner ring of the second outside bearing, are fixed on the rotary member. By interlocking of the bearings, the rotary member slightly moves along the central axis, and at least two of the bearings receive respective preloads with a linkage relationship.