PURPOSE: To prevent the data loss due to a power failure by restoring power within a certain time in case of a power failure of a computer for management and collecting periodically stored data into the storage area of a computer for control to synthesize the trend data.

CONSTITUTION: Plant process values are taken into a computer 1 for control as collected data 12 by an input device 11 and are stored with a data storage area 14 as a ring buffer by periodical data storage processing 13. A computer 2 for management takes collected data 12 into a reception area 24 by periodical data collection processing 22 and sets it to a trend data collection area 21 and records and stores it as time series data. When data is collected at an arbitrary timing, required data is collected from the data storage area 14 to a reception area 25 by arbitrary timing data collection processing 23. This data is arranged in the order of time series by transposition processing 26 and is set to a collection area 21 and is recorded and stored. An execution right 27 is given to these data collection processings in accordance with conditions by switching to correspond to each purpose.