A wavelength selector switch includes first and second refracting plates, an optical splitter, first and second optical systems, an optical coupler polarization controller, and second refracting plate. The first refracting plate refracts the second wavelength-multiplexed light beam. The optical splitter spatially splits into a plurality of wavelength components light beams. The first optical system changes the wavelength components into parallel light beams. The polarization controller selectively changes a polarization angle of each of the parallel light beams. The second optical system condenses the parallel light beams. The optical coupler multiplexes into a third wavelength-multiplexed light beam the parallel light beams condensed. The second refracting plate directs wavelength components of the third wavelength-multiplexed light beam to the first and second optical output ports depending on their polarization angles.