Abstract: The invention relates to a device for adjusting the width of a sieve opening on combine harvesters. The aim of the invention is to be able to economically produce this device and to permit a quick installation of a new sieve or a quick re-installation of the previously used sieve, whereby enabling the previous width of the sieve opening to be immediately readjusted. The invention also aims to be able, while using the device, to adjust the width of the sieve opening on a preliminary sieve from an easily accessible location. To these ends, the lamellas of the sieve are adjusted by means of an adjusting rail, which is actuated by a transversal shaft and by an adjusting mechanism both of which being mounted in a positionally fixed manner on the sieve housing of the cleaning device. The transversal shaft, to which an upwardly oriented driver is attached, is located underneath the sieve.