A control device has a preview image data generating unit, a display unit displaying a preview image, an image formation controlling unit forming an image corresponding to the preview image on a recording sheet, and a user operation detection unit detecting a user operation to make modification in the preview image. The modification in the preview image includes at least one of a change of size of a preview image frame in which the preview image is displayed, a change of an area of the preview image frame, an area of the preview image appeared in the preview image frame. A preview image data modifying unit reflects the user operation detected by the user operation detection unit in the preview image data. The image formation controlling unit forms the image on the recording sheet with reflecting the modification made in the preview image data.