Provided is a wavelength selective switch which includes: at least one input port; a dispersive portion for dispersing wavelength-multiplexed light input from the input port into wavelength-demultiplexed lights; a condenser element for condensing the wavelength-demultiplexed lights dispersed by the dispersive portion; a deflection portion having deflection elements for deflecting, for each wavelength-demultiplexed light condensed by the condenser element; at least one output port for outputting the wavelength-demultiplexed lights deflected by the deflection portion. A light-condensing position shift compensating element is disposed in an optical path between the input port and the dispersive portion or in the dispersive portion, for compensating light-condensing position shift of the wavelength-demultiplexed lights relative to the deflection element, light-condensing position shift being generated based on the arrangement of the input ports.