Abstract: The invention relates to a device for continuous injection under low pressure of a powdered additive into a stream of molten metal.It comprises, in succession from top to bottom:a top compartment 5 for the admission of the molten metal,a treatment chamber 7 connected to the top compartment by a calibrated inlet orifice 8 and in which there opens, on the one hand, a tube 9 connected to a device for injection of powdered additive under gas pressure and, on the other hand, at least one conduit 11 for evacuation of gases, fumes and possible sullage,at least one buffer compartment 6 cooperating with a means for adjusting the discharge rate of the treated metal,a means for collecting the treated metal, for example a mould or a ladle.