Abstract: In a periodic heating radiation temperature measuring technique thermophysical property measuring device that is equipped a heating laser beam irradiator to irradiate laser beams periodically to a sample at a frequency f and an infrared light condenser to condense infrared light radiated from a certain point of the sample, wherein the heating laser beam irradiator and the infrared light condenser being arranged to face each other across the sample, and measures a thermal diffusivity based on a periodic temperature change of the sample, and an infrared fiber that guides infrared light condensed by the infrared light condenser up to a radiation thermometer; and a controller that measures a phase difference ? between a period of a temperature change of the radiation thermometer and a period of the heating laser beams, and calculates a thermal diffusivity based on the phase difference ? and the frequency f.