Disclosed is a thyroid uptake measurement apparatus, in which a radiation attenuation filter is detachably provided at the leading end of a collimator of a radiation detector. The radiation attenuation filter inhibits the saturation of signals when gamma rays exceeding the maximum counting rate are entered. Accordingly, it is possible to inhibit the distortion of signals when the pile-up of the signals increases by an increase in the radiation decay. Moreover, the use of the radiation attenuation filter can significantly improve the scatter fraction, that is, the ratio of scattered radiation/total radiation generated by material scatter of radiation.