Abstract: The turret on a slide of a machine tool is indexible between a plurality of positions in a sequence which is selected by a program. The apparatus for effecting the indexing of turret has a control unit wherein a hydraulic motor can rotate an indexing shaft at different speeds which are determined by the reciprocable spool of a valve regulating the flow of hydraulic fluid from the motor. The spool can be biased against a cam on the indexing shaft by a spring and can be retracted by an electromagnet which is controlled by a decoding unit having several cams on a camshaft which is driven by the turret and several switches which are adjacent to the camshaft.