Abstract: A hinge mechanism for a vehicle seat for adjusting the inclination of the seat back relative to the seat proper. The mechanism comprises: two rigid strength members mounted to pivot relative to each other, one of the strength members being a moving member secured to the seat back and the other being a fixed member secured to the seat proper; at least two slugs adapted to be moved between a position in which they prevent the strength members from moving relative to each other, and a retracted position; and a circular ramp which pivots with the seat back and which can keep a control slug in its retracted position, with the angular sum of the locking angular sector and the unlocking angular sector of the ramp occupying at least 120° about the pivot axis. The invention also provides a seat fitted with such a mechanism.