PURPOSE: To decrease the operating frequency for display of a screen and to quickly display the screen by selecting plural screens via a hierarchy structure.

CONSTITUTION: A hierarchy menu display means 7 takes a sorting menu out of a hierarchy menu memory 4 with a display command of a hierarchical structure control means 5 and displays the menu in an area A of a display device 2. A sorting example, e.g., a boiler system diagram (1) of a desired screen is selected out of the sorting menu under display. Thus the means 7 takes a group menu out of the memory 4 and displays it in an area B of the device 2 with a command of the means 5. Then a desired screen, e.g., a steam temperature distribution (12) is selected. Thus a screen display means 6 takes a screen of a steam temperature distribution out of a screen memory 3 with a command of the means 5. Then the means 6 displays the taken-out screen on the device 2 after erasion of the sorting and group menus. As a result, a desired screen is quickly displayed with a small operating frequency.