PURPOSE: To make a tapping difficult by using a phase distortion generator so as to give distortion to a digital signal at a transmission side and using a phase distortion equalizer correcting the distortion at a reception side.

CONSTITUTION: A voice signal inputted from a microphone 1 is converted into a digital signal by an A/D converter 2. Then in order to be a spectrum within a radio frequency allocation, a phase distortion generator 10 gives a phase distortion through a filter 3 eliminating a high frequency component. The signal is modulated, amplified by a transmitter 4 and the result is radiated from a transmission antenna 5. A reception antenna 6 at the reception side receives the radio wave, demodulated in a receiver 7, and a phase distortion equalizer 11 equalizes waveform distortion generated by the phase distortion generator 10. Then a D/A converter 8 decodes the signal into the original voice signal and the result is outputted from a speaker 9. The tapping is made difficult by adding the phase distortion generator 10 and the phase distortion equalizer 11 to a conventional digital communication equipment in such a manner.