Reactor

A reactor comprising:

• a coil having a wound portion;
• a magnetic core that includes an inner core disposed in the wound portion, the magnetic core forming a closed magnetic circuit;
• and
• a resin mold including an inner resin that is interposed between the wound portion and the inner core, and at least partially covers the inner core, the resin mold not covering an outer-peripheral face of the wound portion;
• the inner core including:
• a basic region having a predetermined magnetic-path cross-sectional area;
• and
• a single middle region having a magnetic-path cross-sectional area smaller than the magnetic-path cross-sectional area of the basic region, the middle region being disposed in a region near a middle portion of the wound portion in an axial direction thereof, the region including the middle portion, the middle region being provided in one core piece, and
• the inner resin is formed by charging a constituent resin into a ring-shaped groove formed by a step between the basic region and the middle region, and includes a thick portion with a thickness larger than a thickness of an area covering the basic region wherein the thick portion includes an area where fluid resin used to form the resin mold portion merges.