A reactor uses a composite magnetic core which combines a ferrite core and a soft magnetic metal core. The reactor is composed of a pair of yoke portion cores composed of ferrite cores, winding portion core(s) disposed between the opposite planes of the yoke portion cores, and coil(s) wound around the winding portion core(s). Flange-like members are disposed at the end part of the winding portion core(s) in a way of being external connected with the periphery of winding portion core(s) which is composed of a soft magnetic metal core. The flange-like member is composed of a metal material with iron as the main component which can be magnetically attracted to a magnet, and a junction portion of the flange-like member and the yoke portion core is formed at one flat plane of the member which is the same plane with an end plane of the winding portion core.