A centrifugal separator for separating solids from a liquid mixture, in which solid particles are suspended in a liquid having a density smaller than that of the particles, which centrifugal separator includes - a rotor having a centre axis, around which it is ratable at a first speed, - a screw conveyor, which is arranged in the rotor and is rotatable around said centre axis at a second speed differing from said first speed, and - a driving device, which is adapted for rotation of the rotor at said first speed and the screw conveyor at said second speed, - the rotor having an inlet for said mixture in the form of at least one inlet channel, which extends into the rotor at its one end, a liquid outlet for separated liquid in the form of at least one outlet channel (12; 66-68), which extends out of the rotor at its said one end, and a sludge outlet for separated solids situated at the opposite other end of the rotor, - the rotor including a conical portion, at the apex of which said sludge outlet is situated, - the screw conveyor being formed for transportation of separated solids through said conical portion of the rotor towards the sludge outlet, - a conveyor shaft is connected with a supporting body, which is arranged within and coaxially with the rotor, and the screw conveyor is releasably supported by the supporting body, the screw conveyor being axially displaceable into and out of engagement with the supporting body, characterised in that - the rotor being rotatably supported only at its said one end through a rotor shaft, which is arranged so that the rotor centre axis extends substantially vertically, - the screw conveyor being engaged for rotation with the conveyor shaft, which extends axially through the rotor shaft and is coupled together with said driving device. - a rotor having a centre axis, around which it is ratable at a first speed, - a screw conveyor, which is arranged in the rotor and is rotatable around said centre axis at a second speed differing from said first speed, and - a driving device, which is adapted for rotation of the rotor at said first speed and the screw conveyor at said second speed, - the rotor having an inlet for said mixture in the form of at least one inlet channel, which extends into the rotor at its one end, a liquid outlet for separated liquid in the form of at least one outlet channel (12; 66-68), which extends out of the rotor at its said one end, and a sludge outlet for separated solids situated at the opposite other end of the rotor, - the rotor including a conical portion, at the apex of which said sludge outlet is situated, - the screw conveyor being formed for transportation of separated solids through said conical portion of the rotor towards the sludge outlet, - a conveyor shaft is connected with a supporting body, which is arranged within and coaxially with the rotor, and the screw conveyor is releasably supported by the supporting body, the screw conveyor being axially displaceable into and out of engagement with the supporting body, characterised in that - the rotor being rotatably supported only at its said one end through a rotor shaft, which is arranged so that the rotor centre axis extends substantially vertically, - the screw conveyor being engaged for rotation with the conveyor shaft, which extends axially through the rotor shaft and is coupled together with said driving device.