The present invention provides a detector which suppress the crosstalk between detector cells while improving the acquisition efficiency of X-ray radiation. The detector includes a plurality of detector cells, arranged along a detection plane of X-ray, in which each detector cell has a scintillator unit made of a scintillator, and a photodiode for transduce the light incoming from the scintillator unit into electric signals. The scintillator units are partitioned each from another by the border, which has a groove extending in the channel and row directions. A scintillator is provided in some part of the border in the incident X-ray direction.