Abstract: A device for evacuation of powder or granular materials stored on sheltered or unsheltered floors or in bins has a fixed frame, at the center of the storage floor or bin, situated above an evacuation orifice and below a protective cap covered by the stored material. The frame serves to support an evacuation mechanism proper comprising two worms of opposite pitch which extend essentially along a diameter of the storage area and which are provided with a continuous rotational movement about their axes and a discontinuous and alternating movement of essentially 180.degree. about a vertical axis.