In order to achieve the good attenuation properties, the electrical conductivity of the compressed stranded wire conductor used as the inner conductor 2 is desirably 99% IACS or more. In the present embodiment, an unplated soft copper wire made of pure copper is being used as the constituent wires 2a of the inner conductor 2 in order to achieve the high electrical conductivity. It should be noted, however, that when the plating has an electrical conductivity of 99% IACS or higher, a soft copper wire subjected to a silver plating for example may be used as the wires 2a. In addition, when the wires 2a are compressed through the die, the wires 2a are subjected to the occurrence of a compressive strain, leading to a lowering in the electrical conductivity, but, by thereafter performing a heat treatment (annealing treatment), it is possible to remove the strain and achieve an electrical conductivity of 99% IACS or higher.

(Insulator 3)

As the insulator 3, it is desirable to use an insulating material having as low a permittivity as possible in order to enhance the high frequency signal transmission properties (more specifically, for example, in order to resist the occurrence of a high frequency signal attenuation in a band of 10 MHz to 6 GHz during long-distance transmission). In the present embodiment, a foamed resin that is provided over the periphery of the inner conductor 2 is being used as the insulator 3. The insulator 3 may be provided in such a manner as to be contiguous to the entire periphery of the outer surface of the inner conductor 2.