PURPOSE: To obtain an instrument wherein grouped information groups are ordered to facilitate a display and a selection by registering, storing, reading out and displaying a plurality of the arbitrary ordered pieces of information.

CONSTITUTION: Signals from a plant are converted to a process quantity by an input processor and stored in a process quantity storage 4 as a plant data base. When, to display, for example, displayed information (i), a displayed information (i) select push button 9b in a displayed information select push button group 8a is depressed, signals indicative of the information (i) are displayed as the information (i) on a display 6 via a displayed information selector and register 7 and a display controller 5. Then, when a displayed information select and register push button 10 is depressed to register a plurality of ordered pieces of information, the displayed information (i) is stored in a displayed information select and register storage 7a. In short, a storing system described here is the one for buffering selection and registration. Accordingly, by repeating the display of selected and registered updated information by depressing a selected and displayed updated information readout push button 10d, outdated information is sequentially displayed (6).