Abstract: A pulse stuffing demand generating device of the kind comprising means for comparing the phases of the write clock signals HDI and the read clock signals HDL of a buffer store in which are written and read multiplexed digital information, the said store having a capacity of n binary digits, wherein the said means comprise first means for comparing the phases of the rising edges of signals HDL and HDI, the said first means supplying a pulse stuffing demand signal when the rising edge of signal HDL is located in the "one" portion of the HDI signal, and second means for supplying a signal authorizing the operation of the said first means, the said signal being supplied when one among n rising edges of the HDI signal is located in the "zero" portion of a signal resulting from the division by n of the HDL signal and the duration of which is equal to one binary digit time slot.