PURPOSE: To constitute an optical multiplexer/demultiplexer without executing the aligning of respective parts at the time of production by unitedly forming an optical waveguide part, an optical fiber supporting part and a grating part supporting part on a substrate.

CONSTITUTION: The titled optical multiplexer/demultiplexer is constituted of a waveguide element forming a projected face on one side wall 26A of a waveguide constituting element formed on the center part of the substrate 20 and forming plural photoconductor arranging grooves 28 on the substrate surface on the opposite side of the side wall 26A, photoconductors 30 fixed on the plural grooves 28 and a grating part 32 having light reflecting periodical grooves 32B on a recessed wall surface 32A engaged and fixed with a projected wall surface on the substrate surface 27 of the side wall 26A side. Consequently, production can be attained without accurate aligning, so that characteristic deterioration can be suppressed, the production cost can be reduced and the mass-productivity can be improved.