A ball screw comprises a shaft, a nut, two return elements, plural rolling elements and a sleeve. When being rotated, the shaft will drive the nut to move and circulate the rolling elements within a circulation path defined by a loaded path and the return passages of the return elements. The nut is provided with a circular groove in an outer circumferential surface thereof, and the sleeve is disposed in the circular groove. The sleeve is provided with plural push grooves in an inner circumferential surface thereof, and there is an angular difference between a rolling passage in the nut and the respective push grooves, and the push grooves cooperate with the rolling elements which pass through the rolling passage. By such arrangements, the push grooves of the sleeve will be pushed by the rolling elements to convert the linear motion into rotary motion, thus making the sleeve rotate.