PURPOSE: To decrease facility cost and circuit cost by arranging a protocol converter which is equipped with various types of means such as terminal communication control, terminal data accumulation, transmitting transfer control, transmitting conversion, transmitting receiving control, receiving conversion and receiving transfer between various terminals without a packet communication function and a packet communication network, and transmitting terminal data.

CONSTITUTION: By a protocol converter 10 which exists and arranged among a facsimile terminal 1, which is a terminal without a packet communication function, a teletype 8 and a data terminal 9 and a packet communication network 5, dividing from the terminal data to the packet data is executed, and integration and reproduction from the packet data to the facsimile terminal are executed, and conversion with a destination address, a sender address and a logical channel number is executed at respective terminals, and a facsimile message is transmitted and received for a packet communication network 5. Thus, respective terminal 1, 8 and 9, non-packet terminal, the communication network is used as it is and the terminal data can be transferred.