In a PET apparatus 1, in a calculation processing unit 50, for each frame, radiation data for a region of interest K of a measurement-subjected part H is extracted, and then the optimum administration rate of a labeled substance T is calculated based on the radiation data such that the radiation concentration for the region of interest K will be steady regardless of the physiological state (blood flow rate etc.) of the subject S. In an administration rate control unit 60, feedback control of the administration rate of the labeled substance into the subject S is carried out based on the calculated optimum administration condition. As a result, the change in the amount accumulated of the labeled substance T in the region of interest K between before and after administration of a drug being tested Y can be obtained easily and precisely in real time as the amount of change in the radiation concentration, and it becomes possible to grasp the measurement results rapidly and easily.