To provide a heating device capable of efficiently and uniformly heating a ring or cylindrical metal coil in a short time.

An iron core wound with a primary coil is made to pass through an inner surface of the ring or cylindrical metal coil formed so that the surface thereof is insulated. Another iron core is wound outside the ring or cylindrical metal coil so as to form a magnetic circuit in a ring together with the forementioned iron core, and the primary coil is wound therearound and connected to a primary power source.