An image-forming device includes a main casing, a drum unit, an image-forming unit, and a transfer unit. The drum unit is detachable from the main casing and includes a photosensitive drum having a rotational axis extending in an axis direction. The drum unit is formed with a plurality of symbols juxtaposed along the axis direction. The image-forming unit forms an image on the photosensitive drum in an image-forming mode. The transfer unit transfers the first developer image onto the photosensitive drum onto a sheet. The image-forming unit forms a first developer image on the photosensitive drum in a maintenance mode. The first developer image transferred onto the sheet divides the sheet into a plurality of regions along the axis direction, the plurality of regions corresponding to the plurality of symbols, respectively.