An image-forming device includes a casing, a process unit, a first shutter, a toner cartridge, a second shutter, and a wall. The process unit is detachably mounted in the casing and formed with a first opening, the process unit having a developer roller carrying a toner. The first shutter opens and closes the first opening. The toner cartridge is detachably mounted in the casing, accommodates the toner, and is formed with a second opening, the second opening being in alignment with the first opening. The second shutter opens and closes the second opening. The wall is disposed between the developer unit and the toner cartridge and is formed with a third opening, the third opening being in alignment with the first opening and the second opening. By providing the wall, the process unit and toner cartridge can be detachably mounted in the casing, thereby avoiding a drop in precision for positioning the process unit and toner cartridge relative to the casing.