PURPOSE: To obtain a microwave attenuator in which a microwave is attenuated by a prescribed attenuation by covering a case to a primary radiator of a parabolic antenna.

CONSTITUTION: A case main body 18 is equipped with a group 10 and a cylindrical attenuation element storage part 20 with bottom and as a material of the case main body 18, a synthesit resin is used, in which the transmission loss of a radio wave is hardly depending on the frequency of the radio wave and which has a property hardly deformed with an external force exerted. A case cover 21 is sticked to the case main body 18 by an adhesives and a synthetic resin similar to that of the case main body 18 is suitable for the material of the case cover 21. In forming an attenuator 4, the case main body 8 is prepared and a radio wave absorbing body 22 cut off into discs is packed in a storage space 23 for containing the attenuation element. The size of the radio wave absorbing body 22 is a size just put in the storage space 23, smaller than the size of mirror face of a parabolic antenna reflection mirror and larger than the aperture of the primary radiator.