An optical transmitter of an optical-wireless hybrid transmission system according to the invention outputs a first single-mode optical signal (center frequency: f.sub.C1) to an optical receiver, generates a polarization-coupled optical signal by orthogonal-polarization-coupling a second single-mode optical signal (center frequency: f.sub.C2) with a third single-mode optical signal (center frequency: f.sub.C3) so as to give the two waves orthogonal polarization directions and the same optical power, and transmits the generated polarization-coupled optical signal to a base station as an optical carrier signal. The optical receiver couples a modulated optical signal transmitted from the base station with the optical signal output from the optical transmitter, demodulates an electrical signal having intermediate frequencies f.sub.IF1 and f.sub.IF2 that is obtained by photodecting a resulting coupled optical signal, and generates transmit-data by filtering a resulting output signal.