Modulators respectively modulate baseband signals into IF signals having
different frequencies. A multiplexer multiplexes the IF signals. An
electrical-optical converter intensity modulates the multiplexed IF
signals into optical signals. A local oscillation signal source outputs a
predetermined local oscillation signal. An external modulator
intensity-modulates the optical signal using the local oscillation
signal. An optical branching portion branches the intensity-modulated
optical signal and respectively outputs branched optical signals to radio
base stations. An optical-electrical converter converts the optical
signal into an electric signal, to obtain an RF signal by
frequency-converting the IF signal. An antenna only transmits a component
having a desired radio frequency extracted in a band filter from the RF
signal to a subscriber terminal. Frequency conversion from the IF signal
to the RF signal is thus optically performed, whereby the frequency or
electrical-optical converter is shared among the radio base stations.