An automatic steering device for self-propelled straddle carriers for lifting and transporting manufactures, includes a spatial portal structure (1) resting on the ground on a plurality of steering wheel units (4) connected by a fifth wheel (14) to the structure above, where each wheel unit (4) includes two tyred wheels (8, 8′) each of which is associated with its own electric motor unit (10, 10′) independently with respect to the other; each electric motor is supplied by its own vector frequency converter controlled by a control unit provided with a control microprocessor; angular rotation of each wheel unit (4) is measured by an incremental encoder integral with the upper structure and with the fifth wheel (14) and connected to the microprocessor.