To obtain a sheet feeder and an image forming device capable of carrying out stable sheet feed by properly blowing air toward a side of a sheet even if the sheet is curled, and sufficiently separating the sheet without an increase of the size and cost of a device.

The sheet feeder is equipped with a paper feed tray 3, a lifting and lowering means of the paper feed tray 3, a side delivery unit 40, a sheet sucking means, and a sheet feeding means. The sheet feeder comprises: a sheet upper limit sensor 43 which detects a side end face of a sheet bundle 2 on the paper feed tray 3, and is disposed in the vicinity of the side delivery unit 40 so that a top face of an upper most sheet S1 on the paper feed tray 3 is in a feed position being a predetermined position; and sheet rear end upper limit sensors 46a-46d or the like capable of carrying out detection within a predetermined range at multiple stages of the height positions of a sensor filler 47 abutting on a rear end of the uppermost sheet S1 on the paper feed tray 3 and an uppermost face rear end of the sheet bundle 2 on the paper feed tray 3.