A wavelength multiplexed light source using multimode interference is provided. The light source includes an input unit for inputting a plurality of incident lights, input waveguides for individually guiding the incident lights, a multimode waveguide having an input edge connected to the input waveguides so that each incident light is coupled at a predetermined position on an output edge opposite to the input edge and an output waveguide connected to the predetermined position. Two incident lights having adjacent wavelengths are arranged relative to a central position of the input edge based on a respective wavelength for the incident light.