PURPOSE: To accurately measure the radioactivity quantity (density) of a measured object without being affected by the temperature condition of a shielding material.
CONSTITUTION: A radioactivity measuring device is provided with a radioactivity detector 11 detecting the radioactivity quantity of a measured object 3 installed in a shielding material 2 stored in a container, a temperature detector 12 detecting the temperature of the shielding material 2, the first A/D converter 13 A/D-converting the output signal from the radioactivity detector 11, the second A/D converter 14 A/D-converting the output signal from the temperature detector 12, and a measuring device 19 constituted of an arithmetic unit 15 receiving the output signals from the A/D converters 13, 14, compensating the output signal from the first A/D converter 13 with the output signal from the second A/D converter 14 for temperature compensation calculation, and storing the calculation result in a memory means as data and an output controller reading the data stored in the memory means and outputting the data to an output means.