PURPOSE: To transmit data without lowering the degree of freedom of memory management by providing a central processing unit, a main storage device, and an I/O device.

CONSTITUTION: An action-start request is outputted from the central processing unit (CPU) A1 of the system A on the data transmission-side to a data transmission control device 10. And the device 10 outputs an interruption-request to the CPU B1 of the system B on the data reception-side. The system B secures an area for storing a transmittal data in the main storage device B2 of itself, and requests to the controlling device 10 for a data transmission. And the device 10 transmits the data from the main storage device A2 of the system A to the main storage device B2 of the system B. After ending the data transmission, the CPU B1 of the system B on the reception-side informs the CPU A1 of the system A on the transmission-side of the ending of the data transmission through the device 10. As a result, the data can be transmitted without lowering the degree of freedom of the memory management.