PURPOSE: To obtain a small-sized dielectric filter which has less passing-band loss by forming a conductor line for band rejection having an attenuating electrode of desired frequency at the outside of the filter band on one lengthwise flank of a dielectric block.

CONSTITUTION: Conductor films 3 are formed on the lengthwise-side reverse surface and both flanks of a dielectric block 1 in a rectangular parallelepiped shape, insertion holes 4∼8 extending from the top to the reverse surface are arrayed, and conductor films 17 are formed on their internal surfaces to obtain a λ/4 resonance element; and insertion holes 9∼12 are further formed halfway among the insertion holes 4∼8. On the end surface 22, a conductor line 18 for band rejection which is in a T shape and has desired impedance and an attenuation electrode of desired frequency is formed to obtain serial resonance with the electrode films 13. This dielectric block 1 is fitted in the recessed part at the bottom of a metallic housing 20; and screws 19 for coupling adjustment are engaged threadably with screw holes 22 formed opposite to the insertion holes 9∼12 of a cover 21, and screws 25 for frequency adjustment are engaged threadably with screw holes 24 formed opposite to the insertion holes 4∼8.