PURPOSE: To make a constant resistance circuit small-sized and to simplify packaging and to reduce the trouble of adjustment, by making the loss quantity of the constant resistance circuit sequential and integrating a resistance part to use it as one block.

CONSTITUTION: Since resistance values of resistances R1∼R4 constituting the constant resistance circuit which is provided in the succeeding stage of a filter and compensates the distortion of the pass band loss characteristic of the filter are determined by the loss quantity for a resonance frequency and a characteristic impedance R0, the loss quantity is made sequential at intervals of 0.25dB from 1.0dB to 3.0dB to limit classifications of resistances. The resistance part consisting of resistances R1∼R4 is integrated, and impedances Za and Zb are connected from the external in accordance with the characteristic.