Child car seat tiltable and rotatable between a travel position and an installation position

The device has a base (11) presenting a vertical part (112) supporting against a backrest of a car seat, and a seat (12) for child, mounted on the base. The part has, in its upper part, a connection zone (14) connected with an upper part of a backrest of the seat (12) in a travel position. Inclination is obtained by rotating the seat (12) in a vertical plane around a fixed point of the connection zone, in the travel position.