PURPOSE: To improve the secrecy of a privacy telephone by sequentially achieving the spectrum inversion and the frequency inversion in accordance with the crypto code which is changed periodically to obtain the cryptic output and the cryptic reproduction output.

CONSTITUTION: A switch 1 is converted to cryptic input position and a switch 2 to cryptic reproduction output position, and a starter switch 5 is turned on. The output from an amplifier AMP to which the cryptic voice signal is inputted, is octosected by mixers M1∼M8 and intermediate band-pass filters BPF1∼BPF8. The cryptic code generated by a cryptic code generator 7 is determined by a present time cryptic code calculation controller 8 by using the time difference between the time lapse from the time when the switch 5 is made on to the present time of the clock outputted by a reference clock generator 6 and the time lapse of the said clock itself until its present time. Accordingly, the non- inversion/inversion frequencies and the substitute frequency are selected by a gate 3 being controlled by a controller 4, and reproduced. As a result, the performance of extremely high secrecy is obtained.