Abstract: The invention relates to an apparatus for adjusting the arching of a resiliently flexible support element for supporting the pelvic and/or lumbar vertebrae in a back rest of a seat including an arching means. According to the invention, a flexible support element is suspended in a seat by multiple guide rods, and a Bowden cable is connected to the support element in such a manner as to arch the support element when traction is applied thereto. A restoring spring draws the support element from its arched position. An intermediate spring is used in combination with the Bowden cable such that the support element resiliently yields to major pressure. Another spring provides compensating forces to counteract the arching adjustment, thereby substantially reducing the force to be exerted in order to adjust the degree of arching.