Auto-document feeder and document feeding method

An auto-document feeder comprising:

• a document placing section on which an original document is placed;
• a sheet detection sensor configured to detect the original document placed on the document placing section, a length in a feeding direction of the original document being a first length larger thap a second length;
• a length detection sensor configured to detect the length in the feeding direction of the original document while the original document is fed;
• a first feeding path for feeding the original document placed on the document placing section to a reading section for reading an image of the original document, a distance from the length detection sensor to the reading section in the first feeding path being larger than the first length;
• a second feeding path for feeding a different sheet of the original document placed on the document placing section to the reading section, the second feeding path being different from the first feeding path;
• a switching section configured to selectively switch between the first feeding path and the second feeding path;
• and
• a control section configured to divert, with the switching section, the original document to the first feeding path if the sheet detection sensor detects the original document.