An image-forming device includes an extension tray and an engaging unit. The cover member is capable of opening and closing thereon. The extension tray is rotatably attached to an upper part of the cover member. The engaging unit engages the cover member with the main casing when the cover member is closed. The engaging unit includes an engagement part, an engaging part, and an operating part. The operating part disengages the engaging part from the engagement part when operated. The operating part is capable of being operated when the extension tray is closed.