In an optical receiver according to the present invention, an input signal light subjected to the differential quadrature phase shift keying (DQPSK) is incident on a PANDA type fiber in a linearly polarized state by 45.degree., so that a delay time difference corresponding to one symbol is generated between orthogonal polarization components in the DQPSK signal light, and then, the signal light is branched by a half mirror into two, to be sent to first and second paths respectively, thereby giving, by a 1/4 wave plate disposed on one of the paths, a relative birefringent amount difference of .pi./2 between the lights propagated through the respective paths. Then, each of the lights propagated through the first and second paths is separated into two orthogonal polarization components by a polarization beam splitter, and the respective polarization components are received by a differential reception circuit so that in-phase components and quadrature components in the DQPSK signal are demodulated. Thus, a small sized and low cost optical receiver capable of stably demodulating the DQPSK signal is provided.