Apparatus for synchronizing the rotating cutter and rotating workpiece of a gear cutting machine, featuring, in one aspect, correcting synchronism errors due to the time lag between application of a command signal and a corresponding movement of the workpiece by delaying or advancing the command signal by an amount dependent on the time lag and, in another aspect, synchronizing circuits which process pulse-encoded measurements of cutter rotation and axial translation to provide a command signal for driving the workpiece.