An image forming device includes: a conveyer that conveys a recording medium; an image former that forms an image on an image carrier and prints the image on the recording medium conveyed by the conveyer; and a hardware processor that controls to stop a print job when a length of the print job reaches a predetermined threshold and form a cleaning pattern image on the image carrier, and at the time of overprinting to further print in an overlapping manner on continuous paper on which a mark image indicating an image formation position is printed, obtains the length of the print job on the basis of an interval between mark images set in advance before starting printing the print job and displays a warning when the length of the print job is estimated to exceed the predetermined threshold.