PURPOSE: To facilitate the adjustment of inductance even when there is irregularity within dimensional tolerance by a method wherein the junction surface at the tip of a leg part is left in an unpolished state, and the junction surface at the tip of the leg part on the opposite side of a coil is formed in a tapered surface inclined toward the inside.

CONSTITUTION: Tapered surfaces 1c and 2c which are inclined toward the inside are formed on the core junction surface on the tip part of the leg parts 1b and 2b on the opposite side of the coil 3 of the U-shaped ferrite cores 1 and 2 having an unpolished junction surface on the tip of the leg part. The leg parts 1a and 2a of the ferrite cores 1 and 2 are inserted into the coil 3, they are connected through the intermediary of a molding material 4, the tapered surfaces 1c and 2c of the leg parts 1b and 2b on the opposite side are opposingly positioned, they are clamped from the back using a clamping metal fitting 7, and inductance is adjusted by applying pressure using the pressure-bonded terminals 5 and 6 from the back of the leg parts 1a and 2a. As a result, the induction can be adjusted easily.