Abstract: The apparatus is of the kind comprising detectors (21,23) of deviation of vehicle positional parameters from a path which is fixed in advance providing electrical data which actuates a control device (14) connected to a steering device (7) for steering the steered wheels (2) of the vehicle. The problem to be solved is to avoid the influence of shocks and vibrations and reduce the interventions of the driver. To this end, the detectors comprise a travelled distance detector (21) and a detector (23) of the steered angle of a steered wheel that provide data to a comparator (28) which is also connected to a memory (30) storing positional data relating to a path to be followed, including a manually set device (43) for introducing the desired spacing between parallel passes.The invention is especially applicable to agricultural machines.