The invention relates to electronic measuring equipment, in particular to a broadband common mode inductor and an isolating circuit comprising the broadband common mode inductor. The isolating circuit comprises an isolating power supply, an input end of the isolating circuit, an input end reference point of the isolating circuit, an output end of the isolating circuit, and an output end reference point of the isolating circuit, wherein the input end or the output end of the isolating circuit is connected with the broadband common mode inductor. The broadband common mode inductor comprises a magnetic core, wherein a coaxial cable is wound on the magnetic core. The broadband common mode inductor is small in differential mode leakage reactance, has good high-frequency characteristic on a differential mode signal, and solves the technical problem that the high-frequency characteristic of the common mode inductor on the differential mode signal is not ideal in the prior art.