This radioactivity analysis device (100) analyzes a radionuclide contained in a measurement sample (1), and is provided with: a radiation detector (2) that detects measurement radiation (101) released from the measurement sample (1); and a radiation analysis unit (10) that analyzes the measurement radiation (101) on the basis of the output of the radiation detector (2). The radiation analysis unit (10) has: a wave height analysis means (12) that extracts a pulse wave height distribution from a pulse signal that is in accordance with the measurement radiation (101) and output from the radiation detector (2); an inverse problem computation means (13) that performs an inverse problem computation on the extracted pulse wave height distribution, and extracts the energy spectrum of the measurement radiation; and a degradation diagnosis means (15) that diagnoses the degradation state of the radiation detector on the basis of the extracted energy spectrum.
