To provide a multi-stage screw carbonization furnace equipped with screw conveyers preventing the thermal deformation of troughs.

There is provided the multi-stage screw carbonization furnace 1 in which screw conveyers 2 heated in a furnace body 3 convey a material to be carbonized by the rotation of screws 8 in cylindrical troughs 20, and the carbonized product is produced through the screw conveyers 2 arranged in the longitudinal direction, characterized in that the trough 20 constituting the screw conveyer 2 is integrally formed of a trough body 21 having a U-shaped cross section in the longitudinal view and a ceiling plate 22 disposed to close the upper opening of the trough body 21; a plurality of beam members 24 spun in the transverse direction crossing the longitudinal direction are joined to the upper opening in the trough body 21; and the ceiling plate 22 is joined to the trough body at portions y1 to y6 in the longitudinal direction and is not joined to other portions.