An automatic document feeder, for transferring a document through a scanning position three times, includes: a first transfer mechanism to reverse a given document via a reversing path, and transfer the same to a scanning position; a second transfer mechanism to transfer the given document from the scanning position to one of a switchback path and a document discharging part; a switchback mechanism to transfer the given document to a lay-by on the switchback path, and then transfer the given document towards the reversing path via a re-entry path; and a control unit to control the mechanisms so that a second original document passes through the scanning position a first time before a first original document passes through the scanning position a third time, and to pause travel of the second original document at the lay-by as the first original document is passed through the scanning position a third time.