PURPOSE: To simultaneously perform branching of wavelength multiplex light, wavelength selection and combining with virtually no losses by making use of the circular conical diffraction phenomena of a diffraction grating in wavelength multiplex optical communication in two directions or multiple directions.

CONSTITUTION: An embodiment of a case in which collimator lenses 50, 51 and a plane diffraction grating are used is illustrated. Light sources 10..., detectors 20... are two dimensionally disposed on the focal plane D of a collimator lens 50, and optical fibers 100, 101... are disposed one dimensionally on the focal plane D of the lens 51, whereby transmission and reception are accomplished.