A sheet feeder is disclosed for feeding sheets from a stack by one sheet in a sheet feeding direction, the one sheet being an uppermost sheet of the sheet stack. The sheet feeder includes: a sheet stacker for accommodating the sheet stack therein; a side fence to regulate side ends of the sheets and movable in a direction perpendicular to the sheet feeding direction; a slide shaft arranged in the side fence and extending in a vertical direction; a link member that swings as the side fence moves, a first end of the link member configured to be slidable along the slide shaft, and a second end of the link member configured to be pivotable about a pivot point, which is arranged on a side wall of the sheet stacker at a position lower than the first end; and a swing stopper unit that stops swing of the link member.