COMMUNICATION SYSTEM COMPRISING A COMMUNICATION LINE MONITOR FOR MONITORING A COMMUNICATION LINE

A communication system includes plural terminal apparatuses and a communication line monitor connected to a common a communication line. The monitor transmits to each of the terminal apparatuses a request signal for requesting each of the terminal apparatuses to transmit the data of a correspondence table, showing a relation between packet data and character codes corresponding thereto, when the monitor is initialized, receives the data of the correspondence table from each of the terminal apparatuses, and stores the received data of the correspondence tables in a memory. Thereafter, the monitor receives packet data transmitted through the communication line, coverts the received packet data into corresponding character codes by referring to the data of the correspondence tables stored in the memory, and displays the converted character codes on a display unit.