Abstract: Diagnosis data for respective portions of an apparatus are collected from respective sensors provided on the apparatus at the respective portions thereof and stored in a memory for each of the respective portions. These diagnosis data are the amount of change with time and frequency of occurrence of abnormal operation. The amount of change with time is yielded from the number of treatments for a detection object of each sensor, while the frequency of occurrence of abnormal operations is provided as a ratio of the number of anbormal operations detected by the respective sensors to the number of treatments by the particular object or part involved. The resulting diagnosis data is compared with a predetermined reference value, and when the diagnosis data exceeds the reference value, a prediction alarm flag indicative of a prediction of necessary maintencance to prevent trouble from occuring is added to the diagnosis data and stored in the memory.