PURPOSE: To smoothen the sliding movement of an inner cable by a method in which a molten resin is extruded into a tubular form from an aperture between a die and a nipple to obtain a casing body and at the same time a metal wire is buried in parallel with the axis in the thick wall of the casing body.

CONSTITUTION: A molten resin is sent into the head 4 of an extruder A by a screw 5 and extruded into a tubular casing 2 from the aperture between a die and a nipple provided in the head 4. At the same time, a wire 3 is supplied from the rear side of the extruder A into the aperture between the die and the nipple while being given a tension by a roller 6 and then buried in the thick wall of the casing body 2 while being tensed straightly. The wire 3 can thus be buried in parallel with the axis in the thick wall of the casing body 2 without weaving.