PURPOSE:To make the reproducibility of data excellent and to reduce data amount by extracting and recording only the data to be considered to be necessary for the evaluation. CONSTITUTION:A data compression preservation device 40 is provided with a change rate calculation part 1 obtaining the change rate for the plant data by the differential amount of data within the prescribed time, a compression period classification part 2 determining the compression period for the change rate calculated by this change rate calculation part with the theshold for compression period classification added by normal fluctuation, a compression period timer part 4 registering the compression period determined by this compression period classification part and outputting a plant data preservation request by this compression period and a data preservation part 3 preserving the data for the plant data by this plant data preservation request, and records a time series signal oblamid from a plant.
