A PET apparatus is provided, which ensures excellent quantitativeness by properly correcting the influence of scattered radiation while improving the resolution of a reconstructed image and keeping good photon pair detection sensitivity. A determining section 52 determines whether a straight line connecting the light-receiving surfaces 15b of a pair of photon detectors 15a which have simultaneously detected a photon pair crosses any one of slice collimators 21_n. When it is determined that the straight line crosses none of the slice collimators 21_n, the corresponding coincidence counting information is accumulated by a first coincidence counting information storage section 53 to generate a signal sinogram. When it is determined that the straight line crosses one of the slice collimators 21_n, the corresponding coincidence counting information is accumulated by a second coincidence counting information storage section 54 to generate a scatter sinogram. An image reconstructing section 60 corrects the influence of scattered components on the signal sinogram on the basis of the scattered sinogram, and reconstructs an image on the basis of the corrected signal sinogram.