PURPOSE: To process a telegraphic message according to a desired priority by providing an AND circuit to a communication control processing device to output a telegraphic message cross detecting signal.

CONSTITUTION: A central processing unit 1 receives/transmits information by conducting read/write to a terminal device 5. This transmission/reception signal is stored in an interface information section 2-2 by a communication control processor 2. This transmission side signal is inputted to one input of an AND circuit 2-1 and the terminal device 5 inputs a signal representing that a modulator-demodulator 3 receives information, i.e., a reception signal to the other input of the AND circuit 2-1 via the modulator-demodulator 3 and a communication circuit 4. Thus, it is when a telegraphic message cross signal is outputted to the AND circuit 2-1 that the telegraphic message represents the cross state on the communication line. A processing section 2-3 receiving the telegraphic message cross signal returns a disable response to the central processing unit 1 and transmits a read instruction to the terminal device when the processing section 2-3 gives a priority to the terminal device 5.