To increase the multiplicity of a signal in an optical transmission line relaying a wireless control station and a wireless base station without being restricted by a configuration condition such as a dynamic range, a noise characteristic on the optical transmission line and a connector or the like for configuring the optical transmission line itself.

Optical digital transmission relays the wireless control station 11 to a plurality of the wireless base stations 31 by multiplexing a downlink digital signal 13c subjected to spread modulation by a specific code unique to each wireless base station 31 on a Q digital signal and each wireless base station 31 extracts the downlink digital signal 13c addressed to its own station from the received downlink digital signal 13c by using an inverse spread code and wirelessly transmits it to mobile stations under its control via an RF section to realize optical multiplex relaying independently of the noise/distortion characteristics and the received dynamic range of a communication system and the condition of the optical transmission line and to enhance the frequency utilizing efficiency in each wireless base station 31.