A load-controlling device controlling load on an optical transmission line, the input of which is coupled to an emitting device for modulating with data and multiplexing a plurality of useful wavelengths into a useful optical signal to be transmitted over the transmission line. The load-controlling device includes elements for generating a filler optical signal composed of at least one filler wavelength that is not modulated by data, to be injected into the optical transmission line. The generating elements generate a source optical signal composed of a plurality of wavelengths corresponding to the plurality of wavelengths of the useful optical signal and selects the wavelength of the filler optical signal among the wavelengths of the source optical signal. A control module controls selection of the wavelength of the filler optical signal depending on information indicative of non-turn-on of a wavelength among the plurality of wavelengths of the useful optical signal.