A ball screw with support devices includes a nut base having two sides equipped with the support devices for providing reliable support for the screw and preventing the screw from deflection. Two runner structures are provided near two ends of the screw. The runner structure includes a driving wheel and a driven wheel having different diameters and concentrically installed. The nut base is connected to the driving wheel via an active connecting element for driving the driving wheel to rotate. The driven wheel moves with the driving wheel and is connected to the support devices via passive connecting elements so that the support devices and the nut displace synchronously. By controlling a diameter ratio between the driving and driven wheels, the nut and the support devices displace with proportional speeds, thereby allowing the support devices to always stay at the two sides of the nut as designed and provide reliable support.