PURPOSE: To prevent the deterioration in a calling quality at the time of transmission with an FDM system transmission line by executing the signal processing timing control in a secret talk receiving part with a clock signal synchronized to a signal processing timing at the transmitting side.
CONSTITUTION: After a transmitting signal echo overlapped to a receiving signal is deleted by an EC 3 , the transmission loss of a transmission line is compensated by an AGC amplifier 4, further, the frequency off-setting at the time of the transmission is compensated by a frequency off-setting compensating circuit 5 and the receiving signal is guided to a secret talk receiving part 7. The control of a signal processing timing in the receiving part 7 is executed by a clock signal synchronized to the signal processing timing at the transmitting part of an opponent device, in which a clock extracting circuit 6 occurs. Thus, the transmission loss, change, variance and change of the calling quality due to the frequency off-setting to occur by the conventional device at the time of the transmission by an FDM system transmission line can be prevented. 9 pilot generating circuit 70 equalizer 83 adder circuit 8 secret story transmitting part a sound signal 71 FFT descrambling circuit 81 FFT scrambling circuit 72,82 frame timing generating circuit.