Disclosed is an image processing apparatus in which image data is generated by a formatter based upon PDL data from a host computer and the image data is output from a printer via an image input/output controller. The apparatus has a scanner unit and a facsimile unit and is capable of transmitting data and of scanning an image while printing is in progress. The formatter senses a service call arising from an error or the like and sends the image input/output controller a request to display this fact. As a result of detection of the error, the image input/output controller halts communication with the formatter and sends a RESET signal to the formatter, whereby the formatter is initialized. Even if an abnormally occurs in a printing function, therefore, recovery of the printing function can be achieved without affecting the scanner and facsimile functions.