A wavelength division multi/demultiplexer multi/demultiplexes incident light to emit demultiplexed lights from each of a plurality of light output ends and includes a first wavelength division multi/demultiplexing circuit having at least one light input end and a plurality of light output end; and second wavelength division multi/demultiplexing circuits of AWG type formed on a substrate, including a plurality of light input and output ends, one or two light multiplexing and demultiplexing sections, and a plurality of arrayed waveguides, and having a transmission bandwidth different from that of the first circuit, the transmission bandwidth indicating the width of a light frequency that can pass through each light input and output end, wherein the first circuit and at least one of the second circuits are optically connected together, and wherein the light output ends of the final second circuit are used as the light output ends of the wavelength division multi/demultiplexer. It is possible to greatly increase the number of channels of the wavelength division multi/demultiplexer using the AWG type wavelength division multi/demultiplexing circuit.