PURPOSE: To set a reconnection starting time point in response to a host connected with a lower rank device by starting the transfer of data after connecting again an interface to a higher rank device from the lower rank device after the interface is separated with a data transfer request received from the higher rank device in the timing preceding the data transfer start time point by an extent equal to the reconnection processing time.

CONSTITUTION: A disk controller 12 serving as a lower rank device containing a host 10 and a data buffer 14 is added to a data transfer control system. A processor 30 of the controller 12 receives a data transfer request from a processor 22 of the host 10, and a transfer control circuit 36 separates an interface, at the time of the starting of the system. Then the reconnection processing time is previously informed to the controller 12 in accordance with the processing speed of the host 10, and the interface is separated with the data request received from the host 10. Then the interface is connected again to the host 10 from a controller 12 in the timing preceding the data transfer starting time point by an extent equal to the reconnection processing time.