An image-forming device may include a casing and a developing unit that is detachably mounted in the casing and formed with a first opening. The developer unit may have a developer carrying member carrying a developer, wherein the developing unit includes one end. The image-forming device may also include a first shutter configured to open and close the first opening and a developer cartridge that is configured to be detachably mounted in the casing, accommodate the developer, and is formed with a second opening. The second opening may be in alignment with the first opening when the developing unit and the developer cartridge are mounted in the casing. The image-forming device may also include a second shutter configured to open and close the second opening. The image-forming device may also include an alignment member between the developing unit and the developer cartridge.