A sheet feeder includes a sheet stacking unit that stacks sheets, a sheet feeding unit that sequentially feeds the uppermost sheet of a stack of sheets stacked in the sheet stacking unit, an airflow supply unit that supplies an airflow to a side surface of the stack of sheets from an opening, a shield member that is disposed between the opening and the stack of sheets and a mechanism that changes the airflow from the airflow supply unit with respect to a stacking direction of the sheets by changing a relative position between the opening and the shield member in a direction other than the stacking direction of the sheets.