To provide a common-mode choke coil which can suppress common- mode current and has little influence on transmission signals, even in a high-frequency (several hundreds of MHz to several GHz).

This coil is provided with a inscribed dielectric substrate 2, forming a dielectric layer inside a hollow of a magnetic body 1 composed of a ferrite core. Two pairs of conductor lines 3, 4 having a parallel plate electrode shape, each functioning as a coil, are provided on both main surfaces of the dielectric substrate 2 which functions as a magnetic core so as to form parallel tracks. The coil is constituted, such that a characteristic impedance Zb formed by a differential mode inductance Le in a minute zone generated by the parallel tracks and the magnetic core and a minute-zone capacitance Cx constituted between the parallel tracks, is equal to a matching impedance Zo. At operation with a common-mode current Ic causing electromagnetic interfering waves, the minute-zone capacitance Cx does not affect, while a combined inductance Lc between the input and the output suppresses the common-mode current Ic.