PURPOSE: To make the filter characteristic more excellent by providing a radio wave absorber for reduction of disturbance of the electromagnetic field mode and the occurrence of the higher-order mode on the inside wall of the case of a filter to reduce the occurrence of noise due to the disturbance of the resonance mode.

CONSTITUTION: A case 8 is made of brass which has the surface plated with gold about 5μm thick. A radio wave absorber 9 is provided on the surface of the inside wall of this case 8. A ferrite having a large magnetic loss is used as this radio wave absorber 9. With respect to this ferrite, an imaginary part of the high frequency permeability is large, and a magnetite, a nickel ferrite, a lithium ferrite, a copper ferrite, a barium ferrite, or the like can be used in the GHz area. In this case, pasted fine particles of a magnetite are printed on the surface of the inside wall of the case 8 with about 100μm thickness to obtain the radio wave absorber.