<p>The phase modulated signal receiver comprises a calculation unit (63) and a control unit (65). The calculation unit (63) determines the input power of a received optical signal on the basis of the current monitored by a monitor circuit (60). According to the ratio of the input power of the received optical signal measured when the delay of the phase reference light outputted from a delay interferometer (51) is a first delay to the input power of the optical signal measured when the delay is a second delay, the calculation unit (63) corrects the monitored current value of when the delay is the second delay to a value corresponding to the input power of the optical signal of when the delay is the first delay. The control unit (65) compares the current value monitored by the monitor circuit (60) of when the delay is the first delay with the current value of when the delay corrected by the calculation unit (63) is the second delay and controls the delay of the phase reference light of the interferometer so that the monitored current may be a local maximum or a local minimum.</p>
