To provide a bearing unit and a thin motor for journaling the same shaft by a pair of bearings, and having a small shaft directional dimension.

In this bearing unit 1, the outer diameter of an outer ring 7 of the second bearing 3 positioned inside the first bearing 2 is constituted smaller than the inner diameter of an inner ring 6 of the first bearing 2. The inner ring 6 of the first bearing 2 and the inner ring 8 of the second bearing 3 are integrally held by an inner ring holder 11, and an outer ring 5 of the first bearing 2 and the outer ring 7 of the second bearing 3 are integrally held by an outer ring holder 10. An engaging part between the outer ring holder 10 and the outer ring 5 is put in a state of being mutually relatively movable in the shaft direction. A disk spring 9 is interposed between the outer ring holder 10 and outer ring 5, and the disc spring 9 is installed so as to apply a constant-pressure preload in the shaft direction of the first and second bearings 2 and 3.