To provide a printed sheet ejection detecting device that can place printed sheets on an ejection tray in a sufficiently aligned condition, even if a large amount of print sheets are printed and ejected on the ejection tray, and an image forming device.

This ejection device 6 as a printed sheet ejection detecting device includes a guide member 36 and an optical sensor 37. The guide member 36 guides a printed sheet P ejected and places it on the ejection tray 35 by turning around a fulcrum A and turning a lower arm portion 36b around a rotation fulcrum B. The optical sensor 36 detects the amount of the printed sheets P placed on the tray 35 by detecting the rotation position of the guide member 36 abutting on the printed sheets P placed on the tray 35. When a printed sheet P is ejected, the guide member 36 bends at the rotation fulcrum B and abuts on the printed sheet P, placing the sheet P on the tray 35 in a desired condition.