PURPOSE: To make it possible to provide a lot of information in such a manner that an operator can see it with ease, by displaying monitoring data and the result of diagnosis compositely on one screen by combination of small screens.

CONSTITUTION: A display screen 1 of CRT has four screen display areas A to D, and the three areas A to C out of them are allotted to first to third monitoring data display areas and the area D to a diagnosis result display area. When abnormality occurs in an apparatus and it is diagnosed by a system, small screen areas showing the results of diagnosis are displayed, the number of the small pictures being the same as that of the obtained results of diagnosis in the diagnosis result display area D. The figure shows the case of three kinds of results of diagnosis being obtained, and the small screen areas 3a to 3c showing the results of diagnosis are displayed in the diagnosis result display area D. In this way, monitoring data and the results of diagnosis can be displayed concurrently. As to the monitoring data, too, it is possible to monitor a plurality of apparatuses simultaneously or to display compositely various data such as the current data on each apparatus and the past records thereof, and thus the accuracy of monitoring can be improved.