A reactor comprises a coil having a winding part, a magnetic core having a plurality of core pieces, and an inside interposed member that is interposed between the winding part and the inside core part of the magnetic core. The reactor is provided with an inside resin part filled into the interior of the winding part. The inside interposed member is provided with a core-holding part that holds thecore pieces in off-center positions relative to the inside interposed member as viewed from the axial direction of the winding part. Taking the direction towards the center of the core pieces from the center of the inside interposed member as the skew direction, as viewed from the axial direction of the winding part, the separation distance between the inner circumferential surface of the windingpart on the skew direction side and the outer circumferential surface of the inside interposed member is greater than the separation distance between the inner circumferential surface of the windingpart on the reverse side relative to the skew direction and the outer circumferential surface of the inside interposed member.