PURPOSE: To make it possible to communicate data mixed with text data and picture data in a real time in duplex by transmitting the data by inserting a switch code in the separation part of text data and picture data.

CONSTITUTION: A communication control part 21 of a host computer 1 and communication control parts 15, 20 of personal computer terminals A, B select whether data to be transmitted is a text or a picture when each of them receives the transmission request of data. In the case of the text, text data is prepared by a text editor and is transmitted. In the case of the picture, picture data is prepared by a graphic editor and is transmitted by inserting a switch code. Each of communication control parts 21, 15, 20 detects the inserted switch code when data is received and displays the data as a text when the switch code does not exist. When the switch code is detected, the display of a picture is performed.