To provide a telephone set which has a wide dynamic range and use optical fibers and realizes satisfactory speaking from a short distance to a long distance.
A frequency modulation reception optical signal ISL inputted from an optical fiber cable through an optical branch coupling means 12 is converted into an electric signal by a light reception module 11 to become a frequency modulation reception signal ISF, and this signal is amplified with a properly set voltage gain α in accordance with the amplitude of the reception signal by a variable gain amplifier 2 to become a frequency modulation reception signal α ISF having a proper amplitude. A frequency modulation reception signal IFL with a carrier frequency F1 as the center frequency is extracted from the frequency modulation reception signal α ISF by a band pass filter 2, and the frequency modulation reception signal IFL is inputted to a frequency demodulator 3 for frequency-voltage conversion through a buffer 14. A reception signal IS demodulated by the frequency demodulator 3 is amplified with a prescribed amplification factor β by a power amplifier 4 to become a reception signal β IS and is outputted as a voice from a speaker.
SASAKI OSAMU
HOSODA TAKUYA
