To prevent double feeding and posture defect, to smooth fork operation and to lessen the generation of spacings between paper sheets by predicting the thickness quantity of the paper sheets to be separated next in accordance with the thickness data measured by a thickness measuring means and controlling the feeding quantity of a feeding member in accordance with the thickness data and the predicted thickness quantity.

The operation control to feed a fork 13 by as much as the thickness measured by a thickness sensor 10 is executed and when the postal items 2 of the same thickness continues for more than a specified number of sheets, bundles 1 of the same postal items are judged to be separated by a control section 15 and the thickness of the postal items to be separated next is predicted. The operation control to feed the fork 13 by as much as the predicted thickness is continued right after the separation until the different thickness is next attained. As a result, the fork can move right after the postal items are separated and the spacing between the postal items 1 to be separated next and a separation belt 4 does not open the spacing (t) even while waiting for the result of the thickness measurement. The double feeding and posture defect are, therefore, prevented at the time of separation of the paper sheets mingled with the various thicknesses and the fork operation is smoothed. The occurrence of the spacings between the postal items is thus lessened.