A superconducting filter including input/output feeders formed on one surface of a dielectric substrate, resonator patterns formed on one surface of the dielectric substrate, and a dielectric plate mounted on the one surface of the dielectric substrate with a plurality of spacers formed on said one surface of the dielectric substrate disposed therebetween. The dielectric plate covers the region including the resonator patterns, and the input/output feeders length-wise over the length within .+-.20% of positive integer times a 1/4 effective wavelength from the sides nearer to the resonator patterns.