To provide a lightweight radio wave-sound wave absorbing thermal insulation body having flexibility and fire resistance, easy in construction, capable of efficiently absorbing a sound wave and a radio wave of a GHz band, having low heat conductivity, and superior in thermal insulation performance.

This radio wave-sound wave absorbing thermal insulation body 10 is composed of nonwoven fabric 3 including a fiber bundling agent 1b composed of an organic substance by 0.1 to 2.0 mass%, formed by bundling a large number of carbon fibers 1a of short fiber, including a carbon fiber bundle 1 having the average fiber length of 31 to 200 mm by 0.1 to 2.0 g/liter in a web and formed by joining a cotton-like fiber web of mixing basalt fiber 2 in its clearance by entwining the mutual fibers by a needle punch, and a skin material 5 of a textile composed of inorganic fiber for covering its almost all surfaces. A radio wave reflecting plate 4 mainly composed of the carbon fiber is arranged on a reverse surface of the nonwoven fabric 3.