To provide a constant velocity universal joint for super-heavy load, and to provide an extension universal shaft to be combined with the constant velocity universal joint so as to be used for a driving unit of a roller of a rolling mill.

This tripod type constant velocity universal joint is formed by supporting a projecting spherical bearing 14 with a shaft 11 through shafts 22 perpendicular to the shaft, which are radially provided at a right angle against an axis 20, and providing the shaft 12 with a bearing holding groove 16 in the axial direction so as to abut on the periphery of the projecting spherical bearing for engagement. The shaft 11 is provided with projecting spherical parts 13 and 23 around a cross point of the center axis and the axis of the shaft 22 perpendicular to the shaft 20, and the shaft 12 is provided with recessed spherical parts 15 and 31 for abutting on the projecting spherical part, and the center axis of both the shaft always cross at the predetermined point with an engagement of the projecting spherical part and the recessed spherical part, and the projecting spherical beating is provided freely to be moved in the axial direction of the shaft 22 perpendicular to the shaft 20. An extension universal joint has a female shaft part and a male shaft part, and has a spline groove provided in one of them so as to transmit the rotation and a rolling bearing brought in contact with a spline groove side surface provided in the other thereof, and has a fitting part having a circular cross section for maintaining the male shaft part and the female shaft part on the same axis at other position.