A multi-computer system includes a plurality of data processors and at least one I/O device which is commonly accessible by the data processors. A plurality of serial bus loops are configurated in hierarchy with interbus linkage devices disposed between adjacent layers of the hierarchy. The data processors are connected to a plurality of first layer serial bus loops and the I/O device which is commonly accessible by the data processors is connected to a second layer of serial bus loop. The interbus linkage devices control linkage among the plurality of serial bus loops and carry out routing control for a start command from the data processor to the I/O device, routing control for an interruption to report the end of I/O device operation, routing control for data transfer, routing control for a request interruption and exclusive use control of the shared I/O device.