PURPOSE: To prevent the leakage of data by providing a means controlling the order of packet by a prescribed definition to the reception and transmission side, deciding the logical channel of each packet in the order of sending at the transmission side and restoring the data string of the packet received from each logical channel at the reception side.

CONSTITUTION: Data X, Y, Z to be sent of data 1, 4, 7 are split at each packet, a transmisson order rule control section 10 is used to share the packets into logical channels A, B, C of data 2, 5, 8. In this case, the sent order is changed according to the sequence restriction of the control section 10. Thus, the packet data are sent in the entirely difference order from that of the packet data constituting the original data 1, 4, 7 to be sent. At the reception side, the packet data received from each logical channel (2, 5, 8) is rearranged by a reception side order rule control section 11 to obtain reception data X, Y, Z of data 3, 6, 7. Thus, the leakage of the data from the transmission line and the decoding are prevented.