A high-frequency signal line includes an element assembly including a plurality of flexible insulator layers, a linear signal line provided in or on the element assembly, a first ground conductor arranged in or on the element assembly so as to be opposed to the signal line not in a first section including a portion of the signal line but in a second section adjacent to the first section, and a second ground conductor provided along the signal line in the first section on the insulator layer on which the signal line is provided. The second ground conductor is not opposed at least in part to the first ground conductor in the first section.