To keep data completely secret by disabling physical reception from the outside by radio although the data were kept secret to some extent before through deciphering, etc.

A directional antenna 24a of a data transmission and reception device A receives even a disturbing wave sent from a nondirectional antenna 25a together with a digital modulated wave sent from a directional antenna 24b of a data transmission and reception device B. The digital modulated wave and disturbing wave received by the directional antenna 24a are supplied to an adder 11 through a switch 26a and added to a phase-inverted disturbing wave from an attenuator 13 to cancel the disturbing wave components and the wave is inputted to a demodulation part 14. When a reception device other than the data transmission and reception device A tries to receive a transmit digital modulated wave of the data transmission and reception device B, a disturbing wave sent by the data transmission and reception device A is also received together with a transmit digital modulated wave of the data transmission and reception device B, so normal demodulation can not be performed because of the disturbing wave to prevent wiretapping.