A nonsense illegal character of a received message is completely avoided, and when the received message can not be correctly displayed, a notice that a language of the message is not supported is given to a user. Use language identification information is imparted to a header portion of a transmission frame of a message. Then, it is judged from the use language identification information whether a character code system corresponding to a language of a received character code string is a character code system supported by a computer. A message corresponding to the received character code string is generated in accordance with the character code system when the character code system is supported. On the other hand, when the character code system is not supported notice information indicating that a message can not be generated is displayed.