To hold satisfactory visibility even at the time of enlarging or reducing a graphics of a plant monitoring device for displaying a system figure.

At the time of reducing a system figure like a figure (a) into a figure (b), a switcher designation 3-15 and a switcher 3-16 is set as a display element whose size is unchangeable and whose position is changeable, and a circuit wiring 3-17 is set as a display element whose size and position is changeable. Only the position of the switcher designation 3-15 and the switcher 3-16 is changed while the size on a screen is not changed even when the screen is enlarged or reduced. On the other hand, the size and position of the circuit wiring 3-17 is changed according to the enlargement/reduction of the screen. Thus, a monitoring screen in which the visibility of information related with the constitution and state of an object to be monitored is held can be displayed even when the screen is enlarged or reduced.