Abstract: An apparatus for producing a double-walled tube of plastic material having an outer corrugated wall and an inner wall connected to the inner crests of the corrugated outer wall, in which an extrusion head is arranged coaxially within mold means formed by a plurality of mold sections traveling along endless paths and abutting along portions of the paths against each other to form a tubular mold having an inner corrugated surface. The injection head comprises two coaxially arranged annular extrusion nozzles having outlet ends axially spaced from each other through which plastic material is extruded.