PURPOSE: To provide the titled mandrel for forming a thin film with limited thickness unevenness by providing a mandrel shaft just in the direction of extruding cover from an extruder to apply sufficiently even for obtaining a thin insulation wire such as enameled wire.

CONSTITUTION: The mandrel is made up of a nipple-shaped head 7, a body 9 and a tail 12. The body 9 is provided with a radial wire rod introduction hole 10 and the circumference of the body and the head is made to serve as a guide path 18 for guiding a cover material to the tip of the mandrel. The tail 12 is provided with a section 14 to receive the cover material extruded from the screw section of the extruder and a feed port 13 is bored therein to guide the cover material to the guide path.