In order to be able to realise single-handed operation when converting the seat arrangement in a foldable rear-seat arrangement in an estate car, a locking device which acts on the back rest is changed over, by means of a catch and a rod, starting from the normal position of the rear-seat structure during the swivelling of a lever coupled to the seat cushion in that the tilting lever of the said back rest is changed over. As a result, the support effect with respect to the rotary catch bolt which secures the back rest is cancelled out and the back rest can be pivoted.