Abstract: An optical receiver, that receives wavelength division multiplexed light including a target channel, includes: a receiver configured to generate an electric signal from input light that includes the target channel; an A/D converter configured to convert the electric signal generated by the receiver into a digital signal; a digital filter configured to filter the digital signal output from the A/D converter with a first frequency characteristic; and a filter controller configured to control a frequency characteristic of the digital filter. The filter controller changes the frequency characteristic of the digital filter from the first frequency characteristic to a second frequency characteristic in stages when a filter control instruction that specifies the second frequency characteristic is given to the filter controller.