In a rare earth metal-based alloy powder supplying apparatus, a rare earth metal-based alloy powder is supplied from a feeder box having an opening in its bottom surface into a cavity by moving the feeder box to above the cavity. The apparatus includes a bar-shaped member which is moved horizontally and in parallel in the bottom of the feeder box. A plurality of the bar-shaped members may be provided horizontally at distances. The apparatus further includes a powder replenishing device for sequentially replenishing the alloy powder into the feeder box in an amount corresponding to a decrement in amount resulting from the supplying of the alloy powder from the feeder box to the cavity, an inert gas supply device for filling an inert gas into said powder feeder box, and a plate member made of a fluorine-contained resin and mounted on the bottom surface of the feeder box. Thus, an alloy powder extremely poor in fluidity and in agitatability and liable to be inflamed can be supplied into the cavity with an extremely uniform filled density without production of agglomerates and bridges and with no fear of inflammation.