To detect an action position of a separating member set on a bundle of documents so as to detect the height of the documents and, on the basis of the detected result, to control a quantity of wind separating the documents on a document mounting part one by one so as to perform a separating function properly without any complication of constitution.

When a start key is turned on after a bundle of documents is placed on a document mounting part, a separating plate solenoid 31 is turned off and a document separating plate 30 is lowered so as to be pressed onto the bundle of documents. Before document paper is fed, a document separation height sensor S14 detects a quantity of reflected light reflected from the document separating plate 30, and the detected value is converted into a document separation height data by means of an automatic paper feeding control unit. If a separating plate return sensor S12 is turned off, a blower motor is set to the respective number of revolutions in compliance with the document separation height data, and a quantity of wind for the document separating unit is controlled, so that the documents can be surely separated by a proper quantity of wind adequate to the height of the bundle of documents.