PURPOSE: To easily grasp a whole system even when the scale of a controlled system becomes large by constituting and displaying the hierarchic structure of a plant which is displayed by using hierarchic information indicated by a retrieved screen identification number.

CONSTITUTION: A display screen control part 25 for the hierarchic constitution diagram of the process monitor device 1 interprets a display screen address inputted from a screen address identification part 17 to judge whether or not there is a display command for the hierarchic constitution diagram and outputs a command signal corresponding to the hierarchic information indicated by the screen identification number of a display screen retrieved in a table to a display screen editing part 27. The editing part 27 refers to the display control table, etc., of the hierarchic constitution diagram in the screen control table 21 to edit and output the hierarchic constitution diagram to a display screen control part 29 and a screen showing the operation conditions of the plant and the hierarchic constitution diagram are displayed on the display device 5, thereby easily grasping the whole system even when the scale of the plant system controlled object becomes large.