a control system of image forming apparatus according to the present invention includes image forming apparatus and a portable maintenance device connectable thereto . the image forming apparatus transmits first condition data indicating conditions of the apparatus to the portable maintenance device when the portable maintenance device is connected thereto , and the portable maintenance device receives the condition data from the image forming apparatus when it is connected to the image forming apparatus . also , the portable maintenance device can be input second condition data indicating conditions of the image forming apparatus , and displays at least one piece of stored guide information on the basis of the first and second condition data .