PURPOSE: To remove an excess release agent of a twisted core, to almost uniformly coat the twisted core with the release agent and to prevent the lowering of adhesion between the twisted core and a housing as in the conventional manner or the occurrence of dimensional errors and the like at the time of peeling off the housing 5 by providing a removing means.

CONSTITUTION: A twisted core 2 coated with a release agent 9 in a storage box 81 is sent to a storage box 11 for the release agent 9, then sent to a removing means 13 for removing an excess release agent 9 through a guide roller 12 provided in the storage box 11, and, after the excess release agent 9 of the twisted core 2 is removed by this removing means 13, the twisted core is sent to a cross head 4 of an extruding machine 3 through guide rollers 14, 15, 16 to form the casing 5.