To prevent magnetism leakage from an upper end joint part between a drum core and a shield core.

The diameter of an upper collar 2a of a drum core 1 wound with a coil 3 is larger than the diameter of a lower collar 2b, and the lower collar 2b of the drum core 1 is inserted in a hole 7 of a bottomed cylindrical shield core 4. In addition, the upper collar 2a is placed on a recessed-step part 6 at an upper end surface of the shield core 4 so as to cover the upper surface of the shield core 4, such that the upper collar 2a is held with a protruding part 5 formed at an upper end periphery of the shield core 4.