PURPOSE: To maintain a data base when a monitor device breaks down and to prevent the occurrence of a trouble in the process control of the monitor device which is restored thereafter by comparing the data base of a computer and that of the other computer and storing/outputting the result.

CONSTITUTION: A data base maintenance control means 10a alters the data base of a data base storage area 11 in accordance with the input of data base alteration data, and stores the number of alteration times for the respective points and data base items in a data base alteration management information storage area 19 by data base alteration data. A data base state judgement control means 20 compares the number of alteration times and the corresponding one of the other computer for the respective points of the data base alteration management information storage area 19 of the computer and for the respective data base items when the computer is started and data base alteration data is inputted. When the number of the alteration times of the computer is larger, the data base is judged to be new and the state is stored in a data base state storage area 21.