data referral and data update on the temporary database 39 the data changed by the database access manager 33 e g updated data are retained in the history database 40 the monitor database 38 is managed by a single server regardless of the status of the main and auxiliary servers 23 24 in a case of failure abnormal state the operation configuration manager 34 of the main server 23 transmits an other server status monitor message to the auxiliary server 24 via the other server communicator 32 as illustrated with an arrow s 1 in fig1 in a case of recovery from the failure it becomes possible for the main server 23 to receive a response to the status monitor message from the auxiliary server 24 when the main server 23 receives the response from the auxiliary server 24 the main server 23 determines that the operation system has recovered and transmits an operation configuration change notice to the auxiliary server 24 illustrated with arrow s 2 in fig1 when the operation configuration manager 34 of the auxiliary server 24 receives the operation configuration change notice via the other server communicator 32 of the auxiliary server 24 the auxiliary server 24 sets the database status to u201c currently switching currently operating u201d and locks the temporary database 39 and the history database 40 then the auxiliary server 24 transmits an operation configuration change possible notice to the main server 23 illustrated with arrow s 3 in fig1 when the operation configuration manager 34 of the main server 23 receives the operation configuration change possible notice via the other server communicator 32 of the main server 23 the main server 23 sets the database status of the operation configuration management memory 41 to u201c currently switching.