An unlimited sliding ball spline therefore includes a spline bearing consisting of an outer cylinder, a ball retainer provided on the inner side of the outer cylinder, and a plurality of balls held by the ball retainer in a plurality of unlimited passages formed on the inner side of the outer cylinder, in such a manner that the balls can be rolled in the unlimited passages; and a spline shaft supported on the plural balls in the spline bearing. The ball spline is capable of making linear, axial reciprocating movements and torque-transmitting rotational movements separately or simultaneously. A circumferential support bearing is disposed coaxially around the outer cylinder and is rotatable with respect thereto and further has a pair of angular contact bearings located on an inner surface thereof. The angular contact bearings are separated by a pre-pressure regulating spacer. A plurality of balls are located circumferentially between each angular contact bearing and corresponding ball rolling grooves on the outer surface of the outer cylinder.