To realize a surface heating inductor in a bottomed hole to heat the neighborhood of the hole bottom sufficiently strong and the remaining part appropriately.

In order to induction heat the inner surface of a water cooling hole 11 of a die 10, the tip side operating part 33 to heat a section of the neighborhood of the hole bottom is constituted of a multiple winding ring in which a metal strip wire 31 is arranged so as to form the orthogonal magnetic flux to the hole axis, and the magnetic center 34 is decentered and arranged closer to the hole bottom inside a wire ring, and the root side operating part 32 to heat the residual section is not wound around by the metal strip wire 31. By this, a magnetic flux density greatly increases at the hole bottom and changes moderately at the other places. Furthermore, the length of the tip side operation part 33 is made twice to five times the hole diameter, counter spacings of the hole bottom are made equal, the counter hole bottom side metal strip wire is made flat, and metallic tubes are constituted to be unicursally arranged in a row.

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