Method and apparatus for preventing unauthorized intrusions into transmission apparatus maintenance system

When an unauthorized log-in is attempted from a maintenance terminal (18) physically connected to one of transmission apparatuses (20, 22, 23, 25, and 27), a log-in process block (34) incorporated in the transmission apparatus (for example, 25) on which the log-in has been attempted counts the number of attempted log-ins (60), and when the number of attempted log-ins reaches a predetermined number, a message reporting the occurrence of an unauthorized log-in attempt is sent to a monitoring terminal (28) for display thereon, together with the network addresses of the transmission apparatus (25) and the transmission apparatus (20) to which the maintenance terminal (18) is physically connected. A list of transmission apparatuses to which a command has been sent from the maintenance terminal (18) is stored in a remote apparatus connection field (62), and when disconnection of a cable of the maintenance terminal (18) is detected by a cable monitor (38), a log-out operation is forcefully performed on the transmission apparatus (20) and also on all the transmission apparatuses indicated in the list stored in the remote apparatus connection field (62).