An automatic document processor for automatically conveying documents includes: a document tray; a document feed path for introducing and feeding originals from the document tray into the interior of a machine; a document pickup roller assembly for picking up originals, page by page, from the document tray; and a document drive roller for conveying originals, and is constructed such that the pickup roller assembly includes two units of document pickup rollers and a pickup roller selecting mechanism for selecting the document pickup rollers to be operated, in accordance with the document size is provided.