PURPOSE: To prevent the stability of an output voltage from deteriorating by forming a gap at a part of the inner peripheral side of the section of a toroidal core, and inserting a high magnetic permeable member into the gap.

CONSTITUTION: A toroidal core 10 has a core section 11 having a gap 15, and a core section 12 having no gap. A high magnetic permeable member 14 is inserted to the gap 15, and a winding 13 is wound on the core 10. Thus, a choke coil which obtained. Further, when the gap is increased, a DC superposing current can be increased, and an arbitrary inductance can be obtained by altering the sizes of the toroidal core and the gaps, and the high magnetic permeable material to be inserted.