A high-frequency signal line includes a laminate of a plurality of insulator layers, a signal line provided on a first principal surface of one of the insulator layers, a first ground conductor provided on a second principal surface of the insulator layer provided with the signal line, the first ground conductor including openings that overlap with the signal conductor, and a second ground conductor provided in or on the laminate so as to be opposed to the first ground conductor with the signal conductor positioned therebetween.