An image-forming apparatus includes a first sheet output tray, an image-reading unit, and an image-forming unit provided below the image-reading unit. The image-reading unit and the image-forming unit form a sheet output space in which the first sheet output tray is provided, and the first sheet output tray includes a top board and a retractable plate provided on a top surface of the image-forming unit. The image-forming apparatus in accordance with the present invention is capable of enhancing sheet alignment capabilities in the case where only a single sheet output tray is used, providing additional sheet output trays having a layer structure, and further providing a sheet-transporting unit.