To provide an optical heterodyne detection system capable of bringing independence from polarized light, and suppressing intensity noise.

An optical heterodyne detection system forms a combined optical signal by combining an input signal 302 and a local oscillator signal 306, and comprises a two-output optical coupler 310 for outputting a 1st beam and a 2nd beam of the combined optical signal; a four-output polarized beam splitter 324 for splitting a beam optically combined with the two outputs based on the polarized state, and outputting two respective polarized parts of the 1st and 2nd beams; a receiver 312 including four optical detectors generating electric signals in response to the four split beams each; and a processor 316 for processing the obtained electric signals.