A sheet feeder includes a separation roller having a circumferential surface that contacts a first sheet to be fed first among stacked sheets and picks up the first sheet and one or more second sheets adjacent to the first sheet, a separation arm that is closer to the circumferential surface of the separation roller downstream in a feeding direction and configured to apply higher frictional resistance to the second sheets than the first sheet to feed the first sheet ahead of the second sheets, and a guide member including a guide portion that has a lower-friction surface than the separation arm and extends from the separation arm with a distal end thereof in contact with or close to the circumferential surface of the separation roller. The guide portion guides the first and second sheets along the circumferential surface of the separation roller.