To provide a simple wiretapping prevention function of which the scale of a circuit is small with no complex soft control.

The number of steps of scrambling, cycle, and initial value of a scramble pattern generation circuit are decided using an access code inputted from a terminal, as a transmission side operation, and scrambling is executed with the main signal to be transmitted for enciphering data. A frame synchronous pattern is set from the access code and multiplexed with the main signal. A part of the information for setting the scramble pattern generating circuit is multiplexed with the main signal as restoration code, as with the frame pattern. On the reception side, a frame synchronous pattern is generated from the inputted access code for synchronizing reception signals. The restoration code separated from the reception signal and the scramble information from the access code set the scramble pattern generating circuit, to generate the same pattern with the transmission side for descrambling, thus restoring a data signal.

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