An apparatus for sensing the density variation of a sliver, includes a sliver funnel through which the sliver passes and which has an intake portion, a discharge portion and a chamber formed as an enlarged part of the discharge portion. The chamber is, through a lateral opening, in communication with a source of pressurized air and a pressure sensing device. The pressure sensing device receives pneumatic signals as a function of the variation of pressure in the chamber dependent upon the density of the sliver portion momentarily present in the chamber. The sliver funnel is arranged at an output of a carding machine for receiving a web discharged thereby and for combining the web into a sliver passing through the chamber. The pressure sensing device comprises a pressure-responsive precision sensor which includes an arrangement for converting the pneumatic signals into digital signals.