To correctly relay a received signal even when a digital modulation signal and an analog modulation signal are mixed as a received signal.

A digital detection part 14 detects an identification pattern stored in a header of a frame constituting a received signal and supplies this detection result to a CPU 25. The CPU 25 judges that the received signal is a digital modulation signal when the digital detection part detects the identification pattern, and judges that the received signal is an analog modulation signal when it does not detect the identification pattern. When it is judged that it is a digital modulation signal, a received signal switching part 15 is controlled so as to connect the digital detection part 14 and a detection signal outputting part 16, and a transmission signal switching part 20 is controlled so as to connect a transmission signal inputting part 19 and the digital modulating part 22.