A transmission line includes, in a stacked insulator in which insulator layers are stacked, a first transmission line portion including a first ground conductor pattern, a second ground conductor pattern, and a first signal conductor pattern, and a second transmission line portion including a third ground conductor pattern, a fourth ground conductor pattern, and a second signal conductor pattern. The first signal conductor pattern extends along the second signal conductor pattern. The first ground conductor pattern and the third ground conductor pattern are provided on different insulator layers and at least partially overlap each other in a plan view.