PURPOSE: To prevent the data transfer from being executed at a low speed by using appropriately a communication buffer in accordance with a characteristic of a communication circuit connected as a communication buffer used in a data communication processor and a data transmission control procedure phase at the time of data transfer.

CONSTITUTION: The system is provided with a circuit defining means 11, a data transfer means 16 and a communication buffer handling means 13. In such a state, with respect to data in a data communication processor, an optimal communication buffer conforming with a characteristic of a communication circuit to which the other data communication processor is connected is selected, the communication buffer is used with high use efficiency, and also, the data in the data communication processor is moved at a high speed and transferred through a communication circuit. In such a way, the communication buffer in the data communication processor can be utilized efficiently, and it is avoided that the processing is complicated in connection with division/assembly of transfer data, and the data transfer becomes a low speed in connection with an increase of the number of times of movement of data.