An optical receiver that demodulates an optical modulation signal into a baseband signal, which is an electrical signal, and decodes a received symbol acquired by converting the baseband signal. The optical receiver includes: an analog-to-digital converter that converts the baseband signal into a digital signal of which the number of samples per received symbol is M/N (samples/symbol), M and N being positive integers, M/N being not an integer, and "M > N" being satisfied; and an adaptive equalization processing unit that executes an equalization operation set in advance to output the received symbol on the basis of the digital signal of which the number of samples per received symbol is M/N (samples/symbol) and a predetermined tap coefficient digital signal equalization tap coefficients used for equalization of a signal, the coefficient being updated in any sampling period.