Abstract: An apparatus for adjusting the arching of a resiliently flexible support element for supporting the pelvic and/or lumbular vertebrae in a back rest of a seat including an arching device comprising a spring and an operating device. The spring is included in the force transmission tract for adjusting the arching. Preferably a spring is fitted between one end of the support element and the force transmission member of the arching means and/or a spring is fitted to the free end of the force transmission member of the arching device behind the operating device.