A sheet feeder includes a tray, a paper feed member, a first detection section, and a second detection section. The tray has a placement surface having an upper surface on which a sheet is placed. The paper feed member is arranged on an entrance side of a sheet conveyance path and conveys the sheet in a conveyance direction. The first detection section detects a leading end side in the conveyance direction of the sheet placed on the placement surface. The second detection section detects a trailing end side in the conveyance direction of the sheet placed on the placement surface. The second detection section is arranged at an end section of the tray on a trailing end side in the conveyance direction.