Transmission line

To provide a lightweight transmission line having excellent flexibility and low transmission loss. A concentric cable (1) constituting a transmission line is provided with an internal conductor (2) and an external conductor (4) provided at the outer circumference of the internal conductor (2) interposed by an insulator (3), the external conductor (4) being provided with an inside conductor layer (40) formed from a first plate member and, outside the inside conductor layer (40), an outside conductor layer (41) formed from a second plate member. The first plate member has a first electrical resistivity and a first thickness and the second plate member has a second electrical resistivity smaller than the first electrical resistivity and a second thickness greater than the first thickness. The first thickness is equal to or greater than the thickness obtained from the skin effect formula at the lowest useful frequency.