A sheet feeder includes: a feeding roller for feeding a sheet; a press member for pressing the sheet against the feeding roller; and a double feed detector for detecting double feed of the sheets when the sheets are fed in superimposition; wherein the feeding roller and the press member are opposed each other at a sheet holding portion for holding the sheet to be fed therebetween, and the double feed detector is placed to be able to detect double feed of the sheets in a region being adjacent to the sheet holding portion, an amplitude of the sheet being suppressed in the region.