PURPOSE: To well follow a corner part and to enhance mounting workability and mounting stability by selecting a synthetic fiber whose set vulcanization temp. rises to a value between the melting temp. and softening temp. thereof as connection yarn and extruding a rubber material by high frequency induction heating to coat the connection yarn before heating a wire insert to the set vulcanization temp.

CONSTITUTION: An insert 1 consists of a corrugated wire 2 and a plurality of connection yarns 3 and, as the connection yarns 3, synthetic fibers whose set vulcanization temp. enters between the melting temp. and softening temp. thereof are selected. The insert 1 delivered from a core delivery reel 11 is introduced into an extruder 13 and an unvulcanized rubber material is extruded to coat the insert 1. The coated insert 1 is successively introduced into a microwave vulcanization tank 15 and a hot air vulcanization tank 17 while taken up by a taking-up machine 19. A high frequency induction heating apparatus 14 is arranged on this side of the microwave vulcanization tank 15 and only the corrugated wire 2 made of steel is heated to the set vulcanization temp. by the induction heating apparatus 14. The contact parts of the connection yarns 3 with the corrugated wire 2 directly receive the heat effect from the wire and the connection yarns 3 themselves are heated by microwave heating to reach the vicinity of the melting temp. thereof.