PURPOSE: To achieve accurate positionig without waveguides for connection, by holding and mounting a dielectric substance resonator at the end toward guide axis with a low dielectric constant thin film, in forming a band block filter through the use of the dielectric resonator in a rectangular waveguide.

CONSTITUTION: A disc shaped dielectric resonator 5 is fixed on the surface of a thin film 4 having low loss and low dielectric constant at usage frequency band of a waveguide such as mica, "Mylar ", and "Teflon ", so that the disc, plane is opposed to the thin film surface, and the thin film 4 is inserted between a rectangular waveguide circuit 6 and a flange 7 and they are fixed with screws 8. With this constitution, the center frequency, band width and amount of rejection as a band block filter can be set to a desired value through the position of the resonator 5 on the rectangular aperture of the circuit 6. It is also possible to insert screws for minute adjustment of the center frequency or amount of rejection of the band-block filter from the outside of a rectangular waveguide E or H wall plane near the dielectric substance resonator.