An optical receiver adapted to receive an optical differential phase modulated signal, the optical receiver for optical space communication comprising: differential light detection means including optical delay interference means for outputting a first optical signal and a second optical signal interfering with each other by controlling, to one bit, a delay between the first optical signal and the second optical signal acquired by splitting the optical differential phase modulated signal, first optical detection means for performing differential light detection on the first optical signal and the second optical signal, and outputting a first main signal, and peak signal detection means (230; 230a; 230b; 230c) for outputting a peak signal indicating intensity of differential light of the first optical signal and the second optical signal; and digital signal processing means including level fluctuation frequency suppression means (320; 320a; 320b) for suppressing a peak fluctuation component on a frequency at which a peak level of the peak signal fluctuates, optical delay interference control means for generating, based on a peak signal having the peak fluctuation component being suppressed, an optical delay interference control signal on which overdrive amplification is performed, and applying the generated optical delay interference control signal to the optical delay interference means, the overdrive amplification being amplifying momentarily the peak signal by push and pull based on an overdrive amplification rate set for the optical delay interference means, and data recovery means for recovering output data, based on the first main signal from the optical detection means. differential light detection means including optical delay interference means for outputting a first optical signal and a second optical signal interfering with each other by controlling, to one bit, a delay between the first optical signal and the second optical signal acquired by splitting the optical differential phase modulated signal, first optical detection means for performing differential light detection on the first optical signal and the second optical signal, and outputting a first main signal, and peak signal detection means (230; 230a; 230b; 230c) for outputting a peak signal indicating intensity of differential light of the first optical signal and the second optical signal; and optical delay interference means for outputting a first optical signal and a second optical signal interfering with each other by controlling, to one bit, a delay between the first optical signal and the second optical signal acquired by splitting the optical differential phase modulated signal, first optical detection means for performing differential light detection on the first optical signal and the second optical signal, and outputting a first main signal, and peak signal detection means (230; 230a; 230b; 230c) for outputting a peak signal indicating intensity of differential light of the first optical signal and the second optical signal; and digital signal processing means including level fluctuation frequency suppression means (320; 320a; 320b) for suppressing a peak fluctuation component on a frequency at which a peak level of the peak signal fluctuates, optical delay interference control means for generating, based on a peak signal having the peak fluctuation component being suppressed, an optical delay interference control signal on which overdrive amplification is performed, and applying the generated optical delay interference control signal to the optical delay interference means, the overdrive amplification being amplifying momentarily the peak signal by push and pull based on an overdrive amplification rate set for the optical delay interference means, and data recovery means for recovering output data, based on the first main signal from the optical detection means. level fluctuation frequency suppression means (320; 320a; 320b) for suppressing a peak fluctuation component on a frequency at which a peak level of the peak signal fluctuates, optical delay interference control means for generating, based on a peak signal having the peak fluctuation component being suppressed, an optical delay interference control signal on which overdrive amplification is performed, and applying the generated optical delay interference control signal to the optical delay interference means, the overdrive amplification being amplifying momentarily the peak signal by push and pull based on an overdrive amplification rate set for the optical delay interference means, and data recovery means for recovering output data, based on the first main signal from the optical detection means.