A maintenance system for image forming apparatuses, which make it possible to acquire appropriate maintenance information even when an exceptional trouble has occurred in an image forming apparatus, to thereby reduce maintenance time and maintenance costs. When an abnormal image occurs in an image forming apparatus connected to a host computer via a network, the image forming apparatus transmits image data of the abnormal image together with supplementary information. The host computer receives the abnormal image data and the supplementary information, and adds these to a database in an HDD. When a transmission request is received from the image forming apparatus, the host computer transmits abnormal image data and supplementary information stored in the HDD to the image forming apparatus. The image forming apparatus receives the abnormal image data and the supplementary information, and displays these on a display unit.