An object of the present invention is to realize an optical gate switch of a monolithic integration type which can avoid problems of losses caused by light coupling of a phase modulation unit to a interferometer optical circuit unit, and can be minimized by integration. The optical gate switch according to the present invention includes an optical waveguide wafer in which a quantum well having a phase modulation effect which is generated by an intersubband transition is set as a core layer; a Michelson interferometer formed on the optical waveguide wafer; and a variable light intensity attenuation unit adjusting a light balance of an interferometer in one of reflection side arms of the Michelson interferometer reflection.