PURPOSE: To provide an optical integrated circuit which shuts off the unnecessary light infiltrating the inside of a waveguide from the outside and simultaneously makes it possible to obtain a material for shutting off this light by an inexpensive process for production.

CONSTITUTION: This optical integrated circuit has a waveguide 5 which is formed on a substrate 1 and consists of a core layer 2 for propagating guided light 13 and clad layers 3, 4 formed in the upper part of this core layer 2 and propagates the guided light 13 coupled to this waveguide 5. The region of a part or the whole covering the upper part of at least the clad layer 4 of the waveguide 5 is provided with a coating layer 19 consisting of a material essentially consisting of a high-molecular compd. and having large light absorbance.