a scanner to read a document and provide image data corresponding to a document image;

a printer to form an image corresponding to the image data provided from the scanner;

an error detector to detect an operating error of the scanner and the printer that are devices;

a controller to stop an operation of the device that cause the error and operate the device only that did not cause the error when the error detector detects the operating error;

means for setting an image forming condition;

means for deciding whether a synchronous control for operating the scanner and the printer in synchronous with each other for every page of document images is used or an asynchronous control for operating the scanner and the printer in asynchronous with each other is used when forming an image based on the image forming conditions that are set by the means for setting;

a first memory to store image data;

compression/expansion means for compressing or expanding the image data; and

a second memory to store the image data compressed by the compression/expansion means,

wherein the image forming apparatus is controlled based on the control decided by the means for deciding,

wherein in the case of the synchronous control, the document image data read by the scanner is stored in the first memory and then, provided to the printer and also compressed by the compression/expansion means and stored in the second memory, in the case of the asynchronous control, the document image data read by the scanner is stored in the first memory, compressed by the compression/expansion means, stored in the second memory, expanded by the compression/expansion circuit, stored in the first memory and then, provided to the printer; and

means for switching the synchronous control to the asynchronous control when the synchronous control is decided by the means for deciding and an error is generated during the image forming operation.