to provide a waveguide type wavelength domain optical switch which makes it possible to use a cheap lens , makes it possible to correct aberration of the demultiplexed wavelengths produced in a plurality of waveguide type demultiplexing circuits , a wavelength domain optical switch is provided with : an integrated element formed by laminating three or more waveguide type demultiplexing circuits ; a first lens for collecting light emitted from the integrated element ; a polarization separation element for separating light emitted from the first lens into x polarization and y polarization and emitting the x polarization and the y polarization at different angles ; a second lens for collecting the x polarization and the y polarization ; a first reflective optical phase modulator for reflecting the collected x polarization and y polarization at any angles ; a ½ - wavelength plate disposed between the second lens and the first reflective optical phase modulator in order to make polarization directions of the x polarization and the y polarization identical ; and a second reflective optical phase modulator for inputting light from the first reflective optical phase modulator into one of the waveguide type demultiplexing circuits .