A synchronizing device for the selection of individual knitting needles in a straight and circular knitting machine to operate according to a desired knitting pattern includes a synchronizing rail of a magnetizable material arranged on a stationary selection needle bed and cooperating with a magneto-resistive sensor arranged on a circulating knitting carriage. The sensor includes a permanent magnet whose magnetix flux is directed perpendicularly to the synchronizing rail, and four magneto-resistive webs arranged side by side in the magnetic flux and at right angles to the direction of circulation of the carriage. The webs are connected in a bridge circuit generating positive and negative analog signals which are compared in comparators with fixed threshold values to generate leading and trailing synchronizing pulses. An additional comparator is provided for detecting the direction of circulation of the carriages.