A coupling structure for coupling to a circuit portion (6) in a coplanar-waveguide circuit (1) having ground conductors (2, 3) at both sides is disclosed. A signal input/output line (4) is provided at the center of the coplanar-waveguide circuit; and an inductive coupling portion (5) having an end of the signal input/output line short-circuited to one of the ground conductors and facing a part of the circuit portion via a first gap is also provided.