To provide a fireproof radio wave absorber having a sufficient radio wave absorbing capability and also a fireproof property as a radio wave absorber for ITS.

The fireproof radio wave absorber has a three-layer structure of a first calcium silicate plate, a second calcium silicate plate containing MnZn-based ferrite and carbon graphite, and a reflector from the incident side of radio waves. The thickness of the first calcium silicate plate is 6-9 mm and the thickness of the second calcium silicate plate is 7-10 mm. The content of the MnZn-based ferrite in the second calcium silicate plate is 50-60 wt% and the content of the carbon graphite is 2-6 wt%. To the incident radio waves of 5.8 GHz, reflection loss at an incident angle 0-80° is 15 dB or more.