PURPOSE: To improve the security of an information transfer device by combining transmission data and random number data with a pseudo noise pattern and adding redundant data to the data so as to prevent leakage of data to other node.

CONSTITUTION: A select section 15 selects and outputs either random data or transmission data based on a PN pattern generated by a PN pattern generating section 13 to make additional arithmetic operation of ciphering. Then a packet header operation section 16 generates a packet by adding control bits DA, SA, USD or the like to the transmission data and sends the result to a transmission line 10. On the other hand, a packet data selection section 17 selects only a jacket including regular reception data based on the DA, USD detected by a packet header detection section 12. Furthermore, a reception data selection section 18 uses a PN pattern generated by the generating section 13 based on a synchronizing signal to discriminate validity of the reception data and only the valid data are received by a terminal equipment 20 to decode the ciphered signal.