PURPOSE: To eliminate a difference in the recognition of process state due to a difference in an operator's personal condition and lessen a burden on an operator by automatically preparing process state data.

CONSTITUTION: A collection means 2 collects process data from a plant 1, and a pre-processing means 3 eliminates a high frequency component from the process data. A local tendency preparation means 4 prepares local data on the basis of the data containing no high frequency component. Also, a macro tendency preparation means 5 prepares macro tendency data on the basis of the process data containing no high frequency component. A state preparation means 6 prepares state data on the basis of the local tendency data and macro tendency data. Then, a display section 7 shows the state data for informing an operator of the state of the plant 1. As a result, the state of the plant 1 can be displayed, regardless of an operator's personal condition, and a burden on an operator can be lessened.