An optical multiplexer/demultiplexer module comprises: a plurality of prisms, each having an inclined surface that is formed by one of the four orthogonal corners of a transparent rectangular solid glass plate being cut and removed at a 45° angle with respect to the end surface; a frame for housing said plurality of prisms; and a plurality of collimator units that convert light having a different wavelength for each prism to collimated light, and inputs the light to the respective prism. When light a having different wavelength is input to a respective prism, the input light is reflected two times, by the inclined surface and a second end surface, after which the light is output from the respective prism. The light that is output from a previous stage prism of the plurality of prisms advances along the same optical path as the light that is output from a later stage prism, so the light that is output from each respective prism is sequentially multiplexed and wavelength multiplexed light is output from the third end surface of the final stage prism.