To automatically deliver unauthorized paper outside a machine, while guaranteeing the normal finish of a preceding job, when detecting the unauthorized paper in an image forming device.

When a printer body part detects that the paper is unauthorized after starting image forming processing to the paper, carrying of the paper is stopped after a predetermined time passes, and the existence of the paper is informed to a system controller (S405). When the system controller receives information, automatic paper delivery processing is indicated to the printer body part and a paper delivery device after completing the processing to normal paper performed by the paper delivery device (S410).