A servo system includes a tubular drive shaft journalled in a housing. A screw is engaged threadably with a nut which is fixed in the drive shaft. A driven body is secured to an end of the screw so that the screw can effect a rectilinear movement with the driven body but cannot rotate. A motor can rotate the drive shaft in an infinite angle through a gearing so that the drive shaft can move in a first direction continuously. Then, an end of a fork is rotated by an abuttment element which is sleeved on the drive shaft. At this time, the other end of the fork activates a hydromechanical servo, and hence a hydraulic driving unit, to move the drive body in a second direction which is equal and a opposite the first direction. After which, the drive shaft is moved back to the original position by the driven body. The driven body is therefore moved a predetermined distance. In this way, the driven body can be moved, accelerated, decelerated and stationary in accordance with the input of the specific numerical control signal.