PURPOSE: To separate freely a memory device from an input/output device by changing the internal interface of the channel device into a serial interface.

CONSTITUTION: A center channel unit 12 reads the control information on a command code, a device address, etc. out of the memory device 11 of a CPU via the memory bus 16 of a parallel data transfer type. Then the unit 12 transmits only the data necessary for input/output interface control to a remote channel unit 13 via a serial data line 17 and in the frame of a serial data type. When receiving this frame, the unit 13 starts an input/output interface action starting with a ADR.OUT signal to an input/output controller 14 by the input/ output interface 18 of a parallel data transfer type. Then the unit 13 receives a STA.IN signal from the device 14 and sends the frame of the serial data type back to the unit 12.