A ceramic scintillator comprises a sintered body of a lutetium oxysulfide phosphor containing at least one element selected from Pr, Tb and Eu as an activator. The sintered body of a lutetium oxysulfide phosphor contains 5 to 15 ppm of an alkali metal element and 5 to 40 ppm of phosphorus. Such a ceramic scintillator can sufficiently make use of the intrinsic characteristics of the lutetium oxysulfide phosphor and has good sensitivity in X-ray detection even when it is downsized.