PURPOSE: To transfer data in a high speed by providing a storage means between transmitting and receiving means different in operation speed and writing data with the transmitting means and reading out written data asynchronously by the receiving means.

CONSTITUTION: When data from an input device end 2 of a transmitting means 10 of a system A or data processed by a CPU8 is transferred to a receiving means 14 of a system B, data is written in a buffer storage means 12 successively through a bus 16. Meanwhile, the receiving means 14 reads out data, which is written in the storage means 12, asynchronously with the transmitting means 10 through a bus 25. Since the operation speed of the receiving means 14 is different from that of the transmitting means 10, CPUs 18 and 26 control them so that the read address does not outpace the write address and the write address does not catch up with the read address.