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.