Although a normal stranded wire conductor being subjected to no compression is more flexible and easier to bend than a single wire conductor, there are many spaces between its constituent wires, and therefore its wires are in point contact. For that reason, in general, the normal stranded wire conductor has a higher conductor resistance and a lower electrical conductivity than those of a single wire conductor having the same outer diameter. By using the compressed stranded wire conductor as the inner conductor 2 as in the present embodiment, the wires 2a are adhered tightly to each other (are in surface contact with each other), with no space between adjacent wires 2a of the plurality of wires 2a. For that reason, the inner conductor 2 using its constituent compressed stranded wire conductor can be lowered in conductor resistance as compared to the normal stranded wire conductor having the same outer diameter. As a result, the inner conductor 2 using its constituent compressed stranded wire conductor achieves the enhanced electrical conductivity and the good attenuation properties. In addition to this, the inner conductor 2 using its constituent compressed stranded wire conductor can maintain the high bendability of the stranded wire conductor, and therefore is resistant to the occurrence of a wire break when bent, as compared to the single wire conductor. Note that, although it is preferable to use the compressed stranded wire conductor as the inner conductor 2, when the normal stranded wire conductor or the single wire conductor can achieve the same action and effect as those of the compressed stranded wire conductor described above, the normal stranded wire conductor or the single wire conductor may be employed as the inner conductor 2.