The invention concerns a device, preferably arranged for setting inclination of a backrest of a seat, primarily a vehicle seat, comprising components which are interconnected in pairs for mutual rotational movement and which are arranged to be associated with the back rest and the seat face, respectively, of the seat. Each component of the pair is formed with a gear rim, the rims positioned adjacent one another in mutual concentric relationship, with the rim teeth meshing with the teeth of a number of planet wheel pairs, the latter rolling in mesh with the associated gear rim, thus causing the two gear rims and their associated component of the joint to turn relatively to one another, and consequently the back rest of the seat to pivot with respect to the seat part.