Reactor

A reactor comprising:

• a coil with a wound portion;
• a magnetic core with an inner core portion arranged inside the wound portion;
• and
• an inwardly interposed member configured to ensure insulation between the wound portion and the inner core portion,
• wherein the inwardly interposed member has a thin portion that is thin as a result of an inner-circumferential surface of the inwardly interposed member being recessed, and a thick portion that is thicker than the thin portion,
• the inner core portion has, on an outer circumferential surface that faces the inwardly interposed member, a core-side projection portion that has a shape conforming to the shape of the inner-circumferential surface of the thin portion,
• the thin portion has a thickness of 0.2 mm to 1.0 mm inclusive, and the thick portion has a thickness of 1.1 mm to 2.5 mm inclusive, and
• the inner core portion and the inwardly interposed member are in substantially intimate contact with each other, and the inwardly interposed member and the wound portion are in substantially intimate contact with each other.