Patent ID: 7848688

Claim:
An image-forming device comprising: a plurality of photosensitive drums arrayed in numeric order in a first direction, each of the photosensitive drums being rotatable and having a circumferential length D, a number of the plurality of photosensitive drums represented by M; a forming unit configured to form a registration mark on each of the photosensitive drums, each of the registration marks formed on each of the photosensitive drums having a color different from one another; an image-carrying member extending in the first direction, the registration marks formed on the photosensitive drums being transferred onto the image-carrying member in the numeric order, the registration marks transferred onto the image-carrying member being arrayed in the first direction, wherein neighboring registration marks are spaced by a distance L in the first direction; a detecting unit configured to detect positions of the registration marks transferred onto the image-carrying member; and a calibrating unit configured to calibrate positions of the photosensitive drums at which the forming unit forms the registration marks, based on the positions detected by the detecting unit, wherein D=N×M×L+(M−1)×L, N being an integer no less than 0.