An image forming machine including a host computer, a printer, a copying machine, and a document supply device for conveying a document printed by the printer to an automatic document feeder of the copying machine, in which a controller is provided for controlling a copy action based on a copy command from the host computer. The controller sends a left-behind document signal when a document is present on document stand of the automatic document feeder, while the host computer shows the presence of the left-behind document on a display when receiving the left-behind document signal from the controller.