An object of the present invention is to provide a radiation temperature measuring device capable of preventing reduction in the accuracy of temperature measurement due to an electromagnetic wave reflected by a measurement target. A radiation temperature measuring device includes a reflective polarizing plate configured to reflect a polarized wave of one direction in an electromagnetic wave radiated from an object to be measured and transmit or absorb a polarized wave of a direction perpendicular to the one direction and an infrared sensor configured to detect the polarized electromagnetic wave of the one direction reflected by the reflective polarizing plate.