A structure supporting a differential rotatably includes an inner ring arranged at the differential, an outer ring arranged at an external peripheral portion formed to surround the differential, and a tapered roller rolling between the inner ring and the outer ring. At least any one of the inner ring, the outer ring and the tapered roller has a carbo-nitrided layer and provides an austenite grain number falling within a range exceeding 10. Thus the structure can be provided with increased anti-crack strength and dimensional stability, and increased rolling contact fatigue life.