PURPOSE: To reduce passage loss as a filter, by arranging an inductance to apply electromagnetic field coupling at a part where strong electromagnetic field exists between a printed circuit board and a resonator.

CONSTITUTION: The resonator 105 made by processing a metallic plate is arranged on the printed circuit board 150 in which a conductor base of earth potential and a dielectric base are superposed, and the end part on one side of the resonator is connected and grounded to the conductor base of the printed circuit board 150 via a through hole. The end part on the other side is connected to the cathode terminal of a varactor diode 111. A covered wire 123 is an inductor which performs the electromagnetic field coupling of the input/output signal of the filter and the resonator 105. Thus, by providing the covered wire 123 at the part where the strong electromagnetic field exists in the resonator 105, it is possible to obtain the strong electromagnetic field coupling, and to reduce the passage loss as the filter.