A transmission line having a slot line with a slot formed on a front surface electrode on a dielectric substrate, and two such slot lines are positioned with the front surface electrodes separated from one another with a gap therebetween. A slot resonator with one end open at the gap side is provided at the front edge side of each slot line, and these slot resonators are positioned so as to be capable of coupling to one another .A slot stub which is branched out from the gap side is provided on each front surface electrode. Thus, leakage of a high-frequency signal in the gap can be suppressed with the slot stub.