A radio wave measurement device enabling highly sensitive measurements of radio waves at an extremely low temperature is disclosed. 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.