PURPOSE: To adjust requests to use a common bus among processors by providing bus use lines as communication lines for the use of the common bus and bus movement lines for showing the movement of the right of bus use among the respective processors.

CONSTITUTION: A processor 51, once detecting the on state of a bus use line 2, stops the driving of a significance line 41 and another tab line 44 to turn off a bus movement line 11. Then, a processor 52 detects the off state of a movement line 11 from the precedent stage to turn off a bus movement line 12 to the trailing stage. A processor 53, once detecting the off state of the movement line 12 from the precedent stage, obtains the right of using the common bus 4, and then handles the request of an adapter 6 through the common bus 4. The processor 53 holds the right of using the bus unless other processors generate a request to use the bus.