A nuclear medical diagnosis apparatus comprising: first and second radiation detectors (1A, 1B) configured to detect gamma rays emitted from a radioisotope in a subject, each detector comprising a plurality of detection elements, wherein each radiation detector (1A, 1 B) is divided into a plurality of groups (G1,... G9) of detection elements, the apparatus further comprising a first energy discrimination unit corresponding to the first radiation detector and a second energy discrimination unit corresponding to the second radiation detector, each energy discrimination unit (2A, 2B) comprising a plurality of blocks, wherein each block in an energy discrimination unit corresponds to a respective group in the corresponding radiation detector (1A, 1B), wherein each block of each energy discrimination unit (2A, 2B) comprises: a coordinate detection portion that extracts position information of the detected gamma ray; an energy discrimination portion; a coincidence determination portion; and an added energy discrimination portion, wherein: the energy discrimination portion is configured to determine whether the energy of electric signals output from the corresponding group of the corresponding radiation detector (1A, 1B) falls within a predetermined energy range and issues a signal proportional to the said energy; the coincidence determination portion is configured to determine if signals output from any two detection elements of the corresponding group have been coincidentally detected on the basis of coincidence in sensing times; and the added energy discrimination portion is configured to add energy values of the pair of the electric signals determined by the coincidence determination portion to obtain a sum of the energy values, and when the sum is equal to a predetermined energy to output a signal proportional to the sum of the energy values, the blocks of each energy discrimination unit being configured to execute arithmetic operations in the added energy discrimination portions in parallel with each other, the apparatus further comprising a coincidence decision unit configured to determine coincidence between the gamma rays incident on the first radiation detector and the gamma rays incident on the second radiation detector, on the basis of outputs from the blocks of the first energy discrimination units and the blocks of the second energy discrimination unit; and an image generation unit configured to generate an image representing spatial distribution of the radioisotope, on the basis of a determination result of the coincidence decision unit and the position information of the detected gamma ray. wherein each block of each energy discrimination unit (2A, 2B) comprises: a coordinate detection portion that extracts position information of the detected gamma ray; an energy discrimination portion; a coincidence determination portion; and an added energy discrimination portion, wherein: the energy discrimination portion is configured to determine whether the energy of electric signals output from the corresponding group of the corresponding radiation detector (1A, 1B) falls energy range and issues a signal proportional to the said energy; the coincidence determination portion is configured to determine if signals output from any two detection elements of the corresponding group have been coincidentally detected on the basis of coincidence in sensing times; and the added energy discrimination portion is configured to add energy values of the pair of the electric signals determined by the coincidence determination portion to obtain a sum of the energy values, and when the sum is equal to a predetermined energy to output a signal proportional to the sum of the energy values,