PURPOSE: To decrease a hardware quantity, to improve reliability, and to reduce costs by respectively providing specific interfaces in plural central processing units, and transferring data between the interfaces in parallel.

CONSTITUTION: An interface 2 provided in a central processing unit 1 is connected to the interface of the other central processing unit. A transmitted data storing means 3 in the interface 2 stores the transmitted data supplied from the central processing unit 1, transmits them in parallel, and after a prescribed time necessary for a serial transfer has been passed since the supply of the transferred data, a transmission control means 4 instructs the central processing unit 1 to supply the next transmitted data. On the other hand, a received data storing means 5 receives the data transmitted in parallel, stores the received data, a reception control means 6 notifies the received data storage to the central processing unit 1, and instructs the unit 1 to reads the received data. Thus the hardware quantity can be decreased, the reliability is improved, and the costs can be reduced.