Each of a plurality of image processing apparatuses includes a module storing unit that stores therein a registered function module and a backup unit that backs up the stored function module and restores a function module based on backup data of the function module. An external storage device stores therein the backup data of the function module. When an error occurs in a first image processing apparatus, the backup unit of a second image processing apparatus restores the function module corresponding to the first image processing apparatus based on the backup data of the function module stored in the external storage device.