PURPOSE: To reduce the time for line program generation by processing various line procedures by a line adaptor and applying transmission/reception with a simple command level to a connection device side.

CONSTITUTION: A simple command sent from a connection device 11 is converted into a line procedure based on the communication rule by a conversion means 17 of a line adaptor 12 and sent to a host computer 16 via modulator-demodulators 13, 14 and a communication line 15 by a transmission/ reception control means 18. The reply from the host computer 16 is received similarly by the line adaptor 12 and prescribed processing by the line procedure is applied, then it is converted into the simple command by the conversion means 17 and sent to the connection device 11. Thus, the processing is attained by the simple command level at the connection device 11 and it is not required to establish a complicated line program.