A transmission line (12) includes a multilayer substrate (20), a signal pattern line (30), a ground pattern conductor (50), and an intermediate ground pattern conductor (40) that is arranged between the signal pattern line (30) and the ground pattern conductor (50) and that is electrically connected to the ground pattern conductor (50). The signal pattern line (30) has a first connection point (30c) to which a signal conductor extending in a laminating direction of the multilayer substrate (20) is connected. A first cavity portion (41h) is formed in the intermediate ground pattern conductor (40) at a position overlapped with a first end portion (30a) of the signal pattern line (30) in a plan view of the multilayer substrate (20). A first end edge (41e) of the first cavity portion (41h) has a first overlapping portion (41a) overlapped with the signal pattern line (30).