System and device for preventing wiretap

1. Field of the Invention A transmitting sequence changing/restoring unit receives, from an ATM control unit, ATM cells stored with the transmitting target information in a segmented state. The transmitting sequence changing/restoring unit groups the cells of this cell string by fours, adds the synchronous cell to the head each group, and changes the sequence thereof. The respective cells are transferred in the changed sequence in sections ranging from the transmitting sequence changing/restoring unit of the transmitting-side ATM node to the unit of the receiving-side ATM node. Accordingly, even if the ATM cell string is intercepted by the third part in this section, this third party cannot reproduce the original transmitting target information. The transmitting sequence changing/restoring unit of the receiving-side ATM node is capable of recognizing where the groups of the received cell string are delimited based on the synchronous cells and restoring the sequence of the ATM cells within the thus recognized group, whereby the transmitting target information can be reproduced.