Abstract: A common-mode choking coil comprises a closed magnetic path core which is formed, for example, by combining two U-shaped cores. Two coils wound in opposite respective directions are mounted on two legs of the closed magnetic path core. These coils are formed by single-layer winding. That is a conductor wire is wound in only one layer, for example, around a bobbin. Then, the bobbins whereon the conductor wire is wound are mounted on the two legs of the closed magnetic path core. For the conductor wire used for the coil, a material having a spring property may be used. Utilizing this spring property of the coil, the closed magnetic path core can be held together by the coil, whereby the two U-shaped cores can be combined. Also, the two coils are identified by colors according to the winding direction of the respective conductor wires.