A compact superconducting filter device can easily change a bandwidth and
a center frequency without changing a pattern or shape of the filter. A
filter pattern is formed on a substrate made of a dielectric material.
The filter pattern is made of a superconductor material. A signal input
line and a signal output line are formed on the substrate so as to extend
from a periphery of the filter pattern. An adjust plate is located above
the filter pattern with a predetermined distance therebetween. The adjust
plate is made of an electrically conductive material.