Automatic sheet feeder

An automatic sheet feeder, comprising:

• a sheet input tray for storing a plurality of sheets including a first sheet and a second sheet, each of the sheets having a front side and a back side;
• a first passageway, a second passageway, and a third passageway, through which the sheets may be successively fed, the first passageway communicating with the sheet input tray, a first end of the second passageway selectively communicating with the first passageway, a second end of the second passageway communicating with the first passageway, and the third passageway selectively communicating the first passageway;
• a sheet-feeding mechanism having a duplex sheet-feeding mode for feeding the first sheet successively from the sheet input tray to the first passageway, the second passageway, the first passageway, and the third passageway;
• and
• a sheet output tray, in which the sheets are stored, communicating with the third passageway, wherein in the duplex sheet-feeding mode, the front side of the first sheet is toward opposite directions when it passes through the first passageway at first and second times, and when the first sheet is fed to the third passageway, the second sheet is fed to the first passageway.