A computer-controlled paper feeder comprises at least first and second supply units from which respective recording materials are supplied one at a time towards a processing station. There is provided a size detector for detecting the size of the recording material contained in respective cassettes inserted in the associated first and second supply units and an emptiness detector for detecting the presence and absence of the recording material in any one of the cassettes in the first and second supply units. These detectors are so correlated with micro-computer that, when the recording material in one of the cassettes has been consumed and the size of the recording material in the other of the cassettes has been found equal to that in the one of the cassettes, the corresponding supply unit is brought into operation to feed the recording material out of the other of the cassettes towards the processing station until the recording material in the other of the cassettes is completely consumed.