PURPOSE: To attain the communication by the fixed length packet system without protocol violation by using a transmission control character and a dummy character in succession to the control character when a message is divided into plural number of filed length packets for the purpose of communication.

CONSTITUTION: When a transmission control DLE character at a sender side is singly an end character of a text, one-preceding character TXn401 and a DLE character 402 are given to a text of a succeeding packet and a dummy character 403 and a dummy character NULL 404 are inserted in the current text and the result is sent. Then the reception station side eliminates the dummy character conversely. Moreover, when the final data of the text is the DLE character 407 and a data DL1046 equal to the DLE character exists just before the DLE character, the three characters together with the preceding DLE character 405 are given to a text of the succeeding packet, and the dummy character DLE403 and the NULL 404 are inserted to the current text and the result is sent. Thus, the communication of the fixed length packet system without protocol violation is implemented.