The disclosed reactor has a case and a cylindrical molded coil assembly which is disposed inside of the case and which is formed by covering a coil with a resin, wherein the coil assembly is sealed by an iron powder mixed resin to which iron powder has been admixed. The reactor has a pillar provided as a single body with the case, and one or multiple ring-shaped core members. The ring-shaped core members are disposed outside the outer surface of the pillar such that the pillar is inserted inside the inner surface of said ring-shaped core members, and the assembly coil is disposed outside the outer surface of the ring-shaped core members such that the ring-shaped core members are inserted inside the inner surface of said coil assembly. The ring-shaped core members are sealed by means of the aforementioned iron powder-mixed resin.