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