The superconducting filter comprises input/output feeders 14a, 14b formed on one surface of a dielectric substrate 10, resonator patterns 16a-16e formed on said one surface of the dielectric substrate 10, and a dielectric plate 24 mounted on said one surface of the dielectric plate 24 with a plurality of spacers 20, 22 formed on said one surface of the dielectric substrate 10. The dielectric plate 24 covers the region including the resonator patterns 16a-16e, and the input/output feeders 14a, 14b length-wise over the length within .+-.20% of positive integer times a 1/4 effective wavelength from the sides nearer to the resonator patterns.