A reactor comprises a reactor core in which two U-shaped core members are connected in a ring shape with gap sections including adhesive layers therebetween, a primary insert-molded resin part which is provided covering leg parts of the core member and which includes joint sections formed around end surfaces of the leg parts a coil placed around the gap sections and the leg parts of the core members, and a secondary insert-molded resin part which is made of a thermoplastic resin and which is insert-molded around the coil to fix the coil on the reactor core and fix the leg parts of the two core members in a connected state, wherein the joint sections of the primary insert-molded resin parts are fitted to each other in a state where the core members are placed connected in a ring shape, to form a peripheral wall surrounding the gap section.