Abstract: A fixed plate supporting the vehicle seat is secured to longitudinal adjusting slides. The fixed plate supports a rotary intermediate plate via a first ball bearing and a cover rigidly connected to the fixed plate and supported at the rotary intermediate plate via a second ball bearing. The assembly is centered on the two ball bearings. Displacement of a central rod is controlled by a lever articulated on a pivot rigidly connected to the fixed plate. This lever is forked and cooperates with the head of the rod and a washer separated from the head by a spring mounted concentrically to the rod. The lever actuates, in one direction, two safety latches normally latching the rotary intermediate plate in order to release the seat for a 180.degree. rotation.