PURPOSE: To increase the effective dielectric constant and to make the resonance frequency of the 1st and final stage to that of the intermediate stage by forming the conductor film being in continuity with the center conductor of a resonance unit of the 1st and final stage onto the surface of an open end of the resonance unit.

CONSTITUTION: Four through-holes 90∼93 and coupling air gaps 110∼112 arranged among the through-holes are provided to a dielectric block 80. Moreover, four side faces and the bottom of the block 80 are provided with conductive films 121, 122 and further adjusting slits 54, 64 adjusting the input coupling and output coupling degree are provided near the final stage through-holes 90, 93. Since the adjusting slit is provided nearby, although the final stage and first stage resonance frequencies are increased, conductor films 141, 142 in continuity with conductive films 100, 103 on the inner face of the through-holes 90, 93 are formed on the surface of the dielectric block 80 to prevent the increased frequency, allowing to increase the effective dielectric constant and to decrease the resonance frequency.