An art includes a core part 10 provided with central leg parts 13A, 13B and right and left leg parts 11A, 11B, 12A, 12B arranged on both sides of the central leg parts 13A, 13B; a coil part 20 formed by winding a conducting wire around a circumference of the central leg parts 13A, 13B; and a heat transfer sheet 30 for dissipating heat in the coil part 20 to outside, in which the coil part 20 is configured in such a manner that a rectangular wire is wound around the circumference of the central leg parts by edgewise winding and a circumference of the coil part 20 wound therearound is abutted on the heat transfer sheet 30.