Optical receiving apparatus and frequency offset compensation method

An optical reception device comprising:

• a local oscillation light source configured to generate local oscillation light,
• a receiver configured to receive signal light of a symbol rate B generated by optically modulating transmission data, perform digital coherent reception by interfering the received signal light with the local oscillation light generated by the local oscillation light source, convert the signal light into an electric digital signal, and output the digital signal, in which a range of an electric band is in a range from-Be to +Be and Be >B/2 is satisfied;
• and
• a digital signal processor configured to demodulate the transmission data from the digital signal outputted by the receiver, wherein
• the digital signal processor comprises:
• a frequency offset compensator configured to estimate a frequency offset amount generated in the digital signal in a range of −B/2 or more and +B/2 or less in accordance with a frequency difference between the signal light and the local oscillation light, and perform frequency offset compensation for the digital signal on the basis of the estimated frequency offset amount to compensate the frequency offset amount in the range of −B/2 or more and +B/2 or less and compensate so as to remain the frequency offset amount of an integral multiple of the symbol rate B when the frequency offset amount is in a range of less than −B/2 and a range of more than +B/2.