Abstract: In case of performing the data transfer between 2 systems respectively operating under different CPUs, it has been traditionally done through I/O interface, and the control of the I/O interface has been done by said CPU.The present invention has been made to implement the data transfer between 2 systems using the data transfer interface equipped with the controller to give and take the dual port memory, and the data between the dual port memory and the outside. Writing from the outside into the dual port memory in this case has been made to be indicated by the flag 1, by which the load of the data transfer of CPU itself is to be retrenched.