A position detector includes a photodetector having photodetecting elements; and a scintillator crystal having uniaxial optical anisotropy. The scintillator crystal is continuous in a uniaxial direction, is disposed on the photodetector such that the uniaxial direction is not perpendicular to the normal to a photodetecting surface, and has a length at least three times the pitch of the photodetecting elements. The uniaxial anisotropy allows at least 4% of scintillation light emitted from a region farthest above the photodetecting surface to reach the photodetecting elements, and allows from 4% to 35% of scintillation light emitted from a region closest to the photodetecting surface to reach the photodetecting elements.