Abstract: The present invention separates radiation from an object by a polarization filter 3 into polarized light beams, causes one of the beams to enter a spectrum analyzer 7 through a first optical path, causes the other to enter the spectrum analyzer 7 through a second optical path, and measures the two-color ratio, while causes radiation of a blackbody 2 placed in a vacuum ultralow temperature thermostatic chamber 1 in a quasi-thermal equilibrium state at an ultralow temperature in vacuo to enter the polarization filter 3 through a third optical path, separates the radiation into polarized light beams, causes the beams to each enter the same optical paths as the respective optical paths for the radiation of the object, causes the beams to enter the spectrum analyzer 7, measures the two-color ratio, and accurately obtains the temperature of the object on the basis of these two two-color ratios.

Abstract: [Problem to be Solved] The present invention provides a radio wave measurement device enabling highly sensitive measurements of radio waves at an extremely low temperature. [Solution] The radio wave measurement device has a radiation-blocking filter through which a targeted radio wave is transmitted, a radio wave-transparent material to reflect a non-targeted electromagnetic wave included in radio waves, and a radio wave detector which are placed in a vacuum vessel, in which the radio waves are transmitted through the radiation-blocking filter, the non-targeted electromagnetic wave included in the radio waves is reflected toward the radiation-blocking filter by the radio wave-transparent material and collected as heat into the radiation-blocking filter, and the heat is exhausted out of the system, allowing the radio waves transmitted through the radio wave-transparent material to be measured with high sensitivity by the radio wave detector.