The high-frequency
signal transmission line (101) includes a resin layer stack (3) having a first resin layer (11, 12, 13) and a second resin layer (21, 22) stacked thereon, a
signal conductor pattern (4) formed on the first resin layer (11), and a ground conductor layer (5) sandwiching part or all of the resin layer stack (3) and opposite to the
signal conductor pattern (4). The Young's modulus of the second resin layer (21, 22) is lower than that of the first resin layer (11, 12, 13). An opening is formed in the first resin layer (12) at least along the position of the signal conductor pattern (4) in the resin layer stack (3), thereby providing a hollow portion (HP) in the resin layer stack (3) by means of the opening.