A screw centrifuge for the continuous separation of flowable substances of different densities includes a rotor drum having discharge openings for the heavy phase that are arranged in a conical portion of the rotor wall, and weir openings for the light phase that are provided on an end wall of the rotor drum. A conveyor screw is rotatable inside the rotor drum and has a screw blade mounted on a hollow shaft for transporting the heavy phase to the discharge openings. A mixture inflow tube is arranged coaxially inside the hollow shaft and leads to a feed chamber in the hollow shaft that is in flow communication with the screw blade. An air extraction member is provided before the feed chamber and generates, in the annular space enclosing the inflow tube, a suction flow co-directional with the delivery direction in the inflow tube.