An optical receiver is provided for reducing in scale the overall system for wavelength division multiplex transmission lines configured redundantly and improving the quality of transmission when the line is switched. The optical receiver includes a variable optical attenuator for controlling an optical loss value for each optical transmission line based on a predetermined optical loss value. A variable dispersion compensation module is also provided for controlling a wavelength dispersion value for each optical transmission line based on a predetermined dispersion value. An optical loss/dispersion controller is also provided for measuring the optical loss value and the wavelength dispersion value of every optical transmission line, outputting the predetermined optical loss value and dispersion value so that the optical loss values and the wavelength dispersion values are equal in all the optical transmission lines, and controlling the variable optical attenuator and the variable dispersion compensation module based on the outputted predetermined values. A receive amplifier is also provided for receiving the optical signal whose light level is kept constant and amplifying the signal. Also, a transmission line switch control module is provided for switching a working transmission line into a protection line if the optical signal level of the working line is lower than a threshold value.