A filter, duplexer, and a communications device have significantly reduced power loss due to the edge effect, and the coupling structure between a resonator and an input or output terminal does not negatively affect the reduction of power loss. A plurality of resonators is provided on a dielectric substrate. Each of the resonators is constituted of a multiple spiral transmission line assembly. At the centers of the multiple spiral transmission assemblies at the input end and the output end, respectively, there are formed coupling pads which are capacitively coupled to associated multiple transmission line assemblies.