The present invention provides a coil component which is possible to be thinner with less leakage flux toward upward and downward directions, and to sustain a good insulation. The coil component comprises a core including two opposing parts mutually opposing, two side legs mutually connect both ends of the two opposing parts, and a middle leg placed between the two side legs and mutually connect central parts of the two opposing parts, a primary coil, which goes around outer circumference of the middle leg, and a secondary coil, which goes around outer circumference of the primary coil, wherein; a distance between outer perimeter edge of the primary coil and inner perimeter edge of the secondary coil varies along circumferential direction.