To reduce user's burden related to operation method and permit general use of data.

A central processing unit 1 comprises a data acquisition function 4 that acquires and stores data of monitoring objects such as a plant or the like, a data conversion function 6 that converts stored time-series data into general data, a data communication function 7 that transmits stored and converted data in HTTP format, being an Internet standard protocol. A monitoring device 8 requests data of the monitoring object to the central processing unit 1 and displays the data in HTTP format sent for the request.