To improve efficiency in a relay amplifier of terrestrial digital broadcast.

In the relay amplifier, a master is connected to a slave by optical cables G1-Gn. In the master, the signal of the terrestrial digital broadcast is inputted by a broadcast inputting means 1, a signal at a prescribed band is extracted from an input signal by broadcast extraction means B1-B8, the extraction signal is amplified to a prescribed level by broadcast amplification means C1-C8, an amplification signal is synthesized by a broadcast synthesizing means 4, a synthesized signal is amplified by a synthesizer amplification means 5, an amplification signal is converted to a light signal by a master light conversion means 6, and the light signal is transmitted to the optical cables G1-Gn by master optical transmission means F1-Fn. In the slave, the light signal is received by slave light reception means H1-Hn, a reception light signal is converted to an electric signal by slave electric conversion means I1-In, and the electric signal is radio-transmitted by radio transmission means L1-Ln.