An apparatus for cultivating microorganisms on a granular medium comprises a vertical cylindrical vessel with a top port for charging the seeded granular medium and a bottom port for discharging the culture. The vessel is separated, heightwise, into sections by horizontal partitions, each section being provided with a tube for letting in an aerating flow of air and a tube for letting out the flow with metabolites. Each partition is composite and made up of partially overlapping circular sectors with perforation in the form of slots.The sectors are provided with a means for shifting them so that when the medium is being charged into a section, all sectors form a solid plate, while, during discharge of the culture from the section, the sectors are shifted so that a free downward passage for the culture is provided.The sector shifting means is located under the partition, relative to the medium, and provides for shifting of the sectors in a horizontal plane. Coaxially arranged with the section is a loosening means whose rake interacts with the culture to keep it loose.