An easily bendable high-frequency signal transmission line includes a dielectric body including a protection layer and dielectric sheets laminated on each other, a surface and an undersurface. A signal line is a linear conductor disposed in the dielectric body. A ground conductor is disposed in the dielectric body, faces the signal line via the dielectric sheet, and continuously extends along the signal line. A ground conductor is disposed in the dielectric body, faces the ground conductor via the signal line sandwiched therebetween, and includes a plurality of openings arranged along the signal line. The surface of the dielectric body on the side of the ground conductor with respect to the signal line is in contact with a battery pack.