Adjustable vehicle seat

The seat has a lifting device (8) comprising an adjustable positioning bead (9) that is made of soft and deformable material. A positioning arm (10) supports the positioning bead. The arm is slidable along a guide device (11) that is secured to an anti-submarining device (3). A rigid movable plate (26) is pivotally mounted on the anti-submarining device so as to cover the bead, where the lifting device and the movable plate are covered by a lining. An upper part (13) of the bead is made of foam.