As the insulator 3, for example, an irradiated cross-linked foamed polyethylene can be used. The degree of foaming in the insulator 3 may be 40 to 70. When the foaming degree of the insulator 3 is 40 or more, its permittivity can be made small, and therefore the high frequency signal transmission properties become good. Further, when the foaming degree of the insulator 3 is 70 or less, the insulator 3 can be prevented from becoming too soft, and therefore becomes resistant to the occurrence of a collapse due to an external force caused in the high frequency signal transmission cable 1 when bent, and the high frequency signal transmission properties become good.

Note that the insulator 3 may be used that includes a foamed layer made of a foamed resin and a non-foamed layer made of a non-foamed resin that is provided over a periphery of the foamed layer. By including the non-foamed layer, when bending the high frequency signal transmission cable 1 or the like, it is possible to prevent the foamed layer from collapsing and it is possible to further suppress the occurrence of a deterioration in the high frequency signal transmission properties.

(Metal Shield Layer 5)

A crack suppressing layer 7 and the plating layer 4 are in turn provided over the periphery of the insulator 3, and the metal shield layer 5 is provided over the periphery of the plating layer 4. The crack suppressing layer 7 and the plating layer 4 will be described later. In the high frequency signal transmission cable 1, the plating layer 4 and the metal shield layer 5 serve as the outer conductor 8.