Abstract: In a network control system connecting terminal units providing at least a chat function to make communication with the other terminal units on a real time basis while connecting the keyboard and executing mutual communication between the terminal units, the terminal unit which becomes the transmitting side describes the mode corresponding to the function to be executed and sets a communication code corresponding to such mode within a communication command to be transmitted. The transmitting terminal indexes a connection timing table and also connects or disconnects the line for communication to the distant terminal unit on the basis of contents of the connection timing table in order obtain cost-effective application of the communication network.