Safety device for a rotatable vehicle seat being locakble in at least two positions

The seat part structure (B) can rotate freely about a vertical axis and relative to a base (A) and carries in its bottom locks (15) able to wedge it in rotation in two opposite positions, either facing the road or back to the road. On one of its sides (10d,10g) is a strike plate (32) for the bolt of a seat belt carried by the seat. The locks are subject to a return spring (27) and are connected to an unlocking control lever (24) articulated under the seat. The safety device has a masking flap (33a) for the strike plate opening (32a) articulated on the side of the seat carrying the strike plate.