PURPOSE: To simultaneously realize functions of privacy telephone communication and tone quality conversion in a cordless telephone set by executing switching of a carrier frequency.

CONSTITUTION: In a spectrum inversion circuit 6 of a transmitting side, a tone quality signal from a transmission amplifying circuit 8 is subjected to spectrum inversion with a carrier frequency obtained by frequency-dividing an output of an oscillating circuit 14 by a variable frequency dividing circuit 12 based on a frequency division ratio set by a control circuit 13 as reference, and the result is inputted to a transmitting circuit 3. In the same way, in a spectrum inversion circuit 5 of a receiving side, a signal received by a receiving circuit 2 is subjected to spectrum inversion with a carrier frequency obtained by frequency-dividing by a variable frequency circuit 11 based on the frequency division ratio set by the control circuit 13 as reference. Accordingly, by setting separately the carrier frequency in transmission and reception, a function for original sound reproduction or tone quality conversion can be realized.