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. The decoding unit selects the direction of rotation of the motor so as to insure that the indexing of turret from a preceding position to the next-following position does not involve a rotation through more than 180 degrees, and the decoding unit further determines the timing of deenergization of the electromagnet to thus enable the spring to urge the spool against the cam on the indexing shaft immediately before a follower of the spool is in register with a notch machined into the periphery of the cam on the indexing shaft and bounded by a surface which effects gradual deceleration of the motor to zero speed. The turret is automatically unlocked from the slide prior to starting of the motor and is automatically locked to the slide when the motor is arrested.