A communication control method in which a communication control unit A.sub.2 in an exclusive communication mode with a communication control unit A.sub.1 receives a requesting frame of an exclusive communication mode or broadcast communication frames from another communication control unit B. Unit B sends a communication frame for announcing an exclusive communication mode after receiving a NAK response from unit A.sub.2, sends message frames after the elapse of a predetermined time T.sub.1, and then sends a frame releasing the exclusive communication mode between Unit B and Unit A.sub.2 after sending the message frames. After receiving the announcing frame from unit B, unit A.sub.2 communicates with unit A.sub.1 to release the exclusive mode between them within the time T.sub.1, enters an exclusive mode with unit B, and then receives communication frames from unit B until it receives the frame of releasing the exclusive mode with unit B. When simultaneous broadcasting frames from unit B are detected, communication control unit A.sub.1, which is in the exclusive communication mode and transmitting message frames to unit A.sub.2, transmits a communication frame for temporarily releasing the exclusive communication mode to unit A.sub.2. The exclusive communication mode between units A.sub.1 and A.sub.2 is revived after unit A.sub.2 receives the casting frames from unit B.