To make a frequency band wide and to improve radio wave absorption characteristics by arranging ferrite absorbers of specified width and thickness continuously in the magnetic field direction of coming radio waves and at a prescribed gap rate in the electric field direction and specifying the dielectric constant of first and second calcium silicate plates.
A calcium silicate plate 2 having the dielectric constant from 5 to 15 is stuck and arranged on the bottom of an aluminum case 1. On the calcium silicate plate 2, a ferrite plate 3 having width A from 15 to 40 mm and thickness B from 5 to 10 mm is continued in the magnetic field direction and arranged at an interval in the electric field direction. A calcium silicate plate 4 is arranged in the dielectric direction of the ferrite plate 3 and fixed by an adhesive agent together with the ferrite plate 3. At this time, the gap rate of the dielectric direction is made into 40 to 55%. The width of the ferrite plate 3 is made wider than 15 mm for reducing the deformation at the time of sintering, the width is made narrower than 40 mm for reducing a reflection loss over wide band and the electric field gap rate is made into 40 to 55% for matching.