PURPOSE: To improve the data transfer efficiency with respect to a data transfer control method which transfer the data between plural host devices and satellite devices via the host buses.

CONSTITUTION: Each satellite device 2 contains a host bus control part 4 which controls the separation/reconnection of a host bus 3. Thus, the part 4 separates the bus 3 when a 1st instruction is issued from a host device 1 and then reconnects the bus 3 when the 1st instruction is carried out in the device 2. Then, the part 4 transfers the data to the device 1. If a 2nd instruction is issued from another device 1 during the execution of the 1st instruction, the part 4 receives the date necessary for execution of the 2nd instruction and separates the bus 3.