A wavelength division multiplexing optical coupler comprising an input optical fiber for a plurality of wavelengths; a lens for converting the light from the input optical fiber into a parallel light; a first optical filter group comprising optical filters aligned along the flux of parallel light so as to be fixed by angles different from each other such that fluxes of light in predetermined wavelength ranges are reflected in respective directions; and output optical fibers, to which the fluxes of light are coupled; wherein a second optical filter group for transmitting the predetermined wavelength ranges are arranged between the first face of the lens and the respective end faces of the set of the output optical fibers for coupling the fluxes of light reflected by the respective optical filters of the first optical filter group.