In a bus system in which a node identifier is allocated to each node, when a data file is transmitted from a transmission node 1 to a reception node 2, a control node 3 issues, to the node 1, a command including an identifier of the node 2 and a field value representing a number of data files to be transmitted to execute the data transfer, and in the case where the number of the data files is 1 or more, after the transmission of the data files of the number specified in the field is completed, the node 1 directs the node 2 to complete the transfer to thereby complete the data transfer, and in the case where the field value is 0, the transmission of the data files is continued, and thus an automatic disconnection mainly led by the data transmission node is adopted after the data transmission, which reduces issuance of commands to the minimum, attaining a high efficiency in processing.