electric motor 14 between the electric motor 14 and the lower middle roll 11 a freewheel backstop 15 is arranged which prevents rotation of the lower middle roll 11 and the lower input roll 10 in a direction against the running direction a of a sliver 16 the lower output roll 12 is driven by an electric motor 17 between the electric motor 17 and the lower output roll 12 a freewheel backstop 18 is disposed which prevents the lower output roll 12 from rotating in a direction opposite to the direction of advance a of the sliver 16 the rpm 39 s of the electric motors 14 and 17 are regulated by an electronic regulating device 19 such that on the one hand in the principal drafting zone between the middle roll pair 11 11 39 and the output roll pair 12 12 39 a draft up to the desired fineness is achieved while on the other hand mass fluctuations of the running sliver 16 are equalized as much as possible the mass fluctuations of the sliver 16 are detected by means of a sensor device situated upstream of the input roll pair 10 10 39 and are as a regulating signal 20 applied to the electronic regulating device 19 the sensor device is constituted by a known rib and groove roll pair 25 through which the sliver 16 runs to cause radial deflections excursions of one of the rolls of.