Abstract: In a polarization diversity receiver comprising demodulator circuits (31, 32) which may have a restricted dynamic range, input intermediate frequency signals are supplied from optical detectors (16, 17) to automatic gain controllers (21, 22) for producing output intermediate frequency signals with their intensities adjusted optimal to the respective demodulator circuits irrespective of a fluctuation which may appear in a polarization state of a signal beam supplied to the receiver. Supplied with the output intermediate frequency signals, the demodulator circuits deliver baseband signals to a signal combiner (43) with their intensities adjusted so as to have a ratio which is equal to a square of a ration between intensities of the input intermediate frequency signals. This makes the receiver have a reception sensitivity which is least deteriorated by polarization diversity.