PURPOSE: To improve the leading characteristics of the attenuation area, by indirectly coupling semicoaxial type dielectric substance resonators with coaxial cables.

CONSTITUTION: A BPF is formed with a shield case 1, inner conductors 21∼26, dielectric substances 31∼36, interstage coupling capacitor forming conductor pieces 41∼410. A coaxial cable 8 has a length an integer multiple of wavelength in wave guide and a coaxial cable 9 has a length and odd number multiple of a 1/2 wavelength in wave guide. On the other hand, coupling elements 10 and 11 couple with a leakage magnetic field of the open end and coupling elements 12 and 13 form a coupling capacitor. The attenuation pole can be produced for the attenuation area by taking suitable degree of coupling for the elements 10, 13, 11 and 12.