Disclosed is a multi-channel array radiation detector that can provide high-definition and high-resolution CT photo-images. The radiation detector has semiconductor photo-detecting elements arranged lengthwise and breadth-wise in a lattice manner and scintillator elements arranged on them one-to-one. The scintillator elements have thin metal light-reflecting material layers formed on side surfaces of the scintillator elements, and a radiation shielding material layer composed of resin blended with heavy metal element particles is filled in between adjacent metal light-reflecting material layers.