A mobile paper guide in an automatic document feeder (ADF) is comprised of draft platen, motor, connection rod, and paper guide plate; the rod including a knob inserted onto the rod, an arm extending from the knob for the rod to rotate as driven by platen; the rod and the platen engaging turns against each other when the rod is limited; the plate movably disposed to the arm; ADF having a chute above the paper guide; and the paper guide moves up and down therein to retain and align paper sheet.