Abstract: A window displaying method suited to the monitoring and operating of the runs of a plant is provided. A display area whose display content is comparatively unimportant is selected from within each of a number of process monitoring frames, and it is registered beforehand as a window area capable of opening a window. In a window display mode, the window is opened in the registered window area, and a window frame is displayed in the window. Thus, an appropriate window display which does not hamper necessary monitoring information can be automatically realized without the operator's needing to carry out window movement, etc. Individual areas for the respective run stages of the process of the plant may well be registered as such window areas.