A sheet feeder includes an ejection tray, an ejector, an aligner, a pressing member, a friction member, and a switching device. The ejection tray stacks sheets. The ejector ejects a sheet to the ejection tray. The aligner is disposed downstream of the ejector in a direction of ejection of the sheet. The aligner is rotatable in a normal direction and a reverse direction. The pressing member applies pressure between the sheet and the aligner to enable the aligner to convey the sheet by rotation in the normal direction and the reverse direction. The friction member contacts the sheet ejected on the ejection tray to prevent conveyance of the sheet. The switching device switches contact and separation of the friction member with respect to the sheet.