A reactor including a coil having a wound portion that is formed by winding a wire, a magnetic core having an inner core portion disposed inside the wound portion and an outer core portion disposed outside the wound portion, the inner and outer core portions forming a closed magnetic circuit, and an inner resin portion that joins an inner peripheral surface of the wound portion and an outer peripheral surface of the inner core portion to each other. The inner core portion includes a plurality of core pieces and gap portions that are constituted by a portion of the inner resin portion, the core pieces each including a gap-facing surface that faces a corresponding gap portion, a coil-facing surface that faces the inner peripheral surface of the wound portion, and a notch-shaped resin flow portion at a corner portion between the gap-facing surface and the coil-facing surface.