PURPOSE: To attain ease of maintenance, by displaying a kind, unit and format of data on a man-machine connecting device, reading a data inputted from the device to a data area, and changing the data being the objective of maintenance.

CONSTITUTION: The information with key input by the operator is read on a screen of a CRT1, and when the information is a generic name of data relating to equipment to be extended, the corresponding information is obtained. Further, the data name and the unit of key input location data are displayed on the screen of the CRT13. When the key input is performed to the designated location by the operator, the information is written in the corresponding data area. Thus, the data correction relating to the extended equipment, i.e., the maintenance is attained.