A transmission line includes connecting portions connected to the outside and a main body located between the connecting portions. Each of the connecting portions includes a terminal electrode connected to an external electrode, a signal conductor, and ground conductors. The main body includes the signal conductor and the ground conductors, and at least one of the plurality of connecting portions includes a first region including the terminal electrode, a second region adjacent to the first region along a signal propagation path, and a third region located between the second region and the main body. The first region, the second region, and the third region provide impedance matching at the connecting portion.