System of automatic guidance of vehicles by means of the detection of changes of the dielectric properties in a pre-recorded rail-guide, wherein the dielectric changes are detected by a high resolution radar device and wherein there is a control system of the vehicle that has the ancillary means required to convert it to an auto guidance system characterized in that the system is composed by a pre-recorded rail-guide (1) an information reading device (11) and auxiliary means of vehicle control (12).