PURPOSE: To operate a personal computer and a printer without malfunction under a same environment independently of the communication distance by interrupting signals other than transmission data as part of the transmission data.

CONSTITUTION: Transmission data and a data strobe signal from a personal computer are respectively fed to a data transmission reception section 10 and a data control signal conversion section 30 from input output terminals 1, 2. Furthermore, a control signal from the personal computer to a printer is fed to the conversion section 30 via a control signal transmission reception section 20. Then the conversion section 30 converts the transmission data of the inputted parallel interface signals into serial interface signals and sends the converted signals to a signal level conversion section 40. The conversion section 40 converts the input signal into a communication signal and transmits the converted signal to an opposite equipment. Furthermore, the conversion section 30 converts the control signal into character codes not used for printer control codes and other than character codes of the transmission data and converts the converted codes into serial interface signals similarly to the case with the transmission data and transmits the converted signals as part of the transmission data.