PURPOSE: To attain the connection between all terminal devices and a host computer by using a code converting ROM to convert a character data inputted from a line into an object code.

CONSTITUTION: A data transmitted from the host computer 3 is received by a communication controller 6, where the data is subject to serial/parallel conversion. A CPU13 references a code converting table ROM8 to convert a data of the communication controller 6 into an object code and transmits the result to a terminal device 2. Further, a data not stored in the ROM8 is converted into the object code by referencing an external registration RAM9 and transmits the result to the terminal device 2.