A car seat is provided with fold-down seatbacks and an associated safety-belt system. The shoulder belt of the safety-belt system in the upper corner of the seatback from the direction of the outside of the car, exits through a slot-like opening of a covering on the seatback in the direction of the belt user, and a seatback release is arranged at a distance from the safety-belt deflector. So that the seatback release does not have to be configured and built individually for car seats of the most varied kinds, a unit which is mountable on the contour of the seatback and accommodates the belt deflector and the seatback release, is prefabricated as an assembly unit.