PURPOSE: To ensure the preload to prevent the generation of a backlash by rotating and driving a driving cam member by a driving motor, and linearly moving a load carriage engaging the same with cam followers.

CONSTITUTION: A driving cam 48 is rotated and driven by a driving motor 22 through a ball spline shaft 52, and a load carriage assembly 40 is linearly moved along the guide tracks 34a, 34b together with the driving cam 48 in a state that a cam rope 80 is successively engaged with the cam roller followers 38 projected on a track support 36 at specific pitches. On this occasion, the driving cam 48 is short in length, and in a recirculation drive ball 62 of a slide ball mechanism 49, the preload is applied to a driving rib 54 of the ball spline shaft 52 in the assembling to prevent the generation of the backlash. Whereby the life of the cam roller followers can be elongated.