To provide an optical receiving unit capable of being downsized with a simple configuration for the DQPSK polarized wave multiplexing scheme and the power consumption and cost of which are small.

The optical receiving unit separates DQPSK polarized wave multiplexing signal light S into each signal light SH, SV of horizontally/vertically polarized waves with a polarized wave beam splitter 3 and branches each signal light SH, SV into two using photo couplers 4H, 4V. Then, one group consiting of the branched light SHI, SVI from the respective photo couplers 4H, 4V is given to a delay interferometer 5I on the I branch side via optical circulators 10I1, 10I2 so as to be propagated in both directions while, the other group consisting of the branched light SHQ, SVQ from the respective photo couplers 4H, 4V is given to a delay interferometer 5Q on the Q branch side via optical circulators 10Q1, 10Q2 so as to be propagated in both directions, and thus a pair of the delay interferometers 5I, 5Q is shared by horizontally/vertically polarized waves.