PURPOSE: To use this plant monitoring device for plant operation management in a usual state and to use the device for plant monitoring only when it is required by providing the device with a means for displaying an interruption on a display screen and a means for temporarily storing plant operation management processing.

CONSTITUTION: A plant monitoring processor 3 always monitors the state of the plant 1 through a process input processor 2. When the status of the plant 1 requires operator's monitoring, e.g. when a process value to be monitored is being approached to an alarm limit value, the processor 3 judges the state and informs an interruption processor 6 of the judged result. At the point of time, a plant operation managing processor 5 judges whether the processing is being executed or not, and when the processing is being executed, the processor 6 temporarily stores the plant operation managing processing and displays a screen for plant monitoring while leaving a part of the plant operation management processing image. Consequently the plant monitoring device can execute plant operation management in an usual state and execute plant monitoring only when it is required.