Abstract: The method of and device for controlling the roll exchanging operation in an unrolling device includes the provision of a set of control numbers computed from the counted number of revolutions of the old roll and from the length of the withdrawn web prior to the initiation of the roll exchanging operation; the control numbers are computed from two intervals of the measured web length, from corresponding intervals of the counted number of revolutions, from the thickness of the web, from the feeding speed of the web, from the time constents of the control elements of the roll exchanging device, from the length of the adhesive leading edge of the new roll, from the desired length of the residual trailing end portion of the old web and from the diameter of the supporting central reel; computed control numbers are stored and compared in a comparator with the actual number of revolutions of the old roll whereby the coincidence of the actual number with the stored number generates in a control unit a control signal