The X-ray detection device according to an aspect of the present disclosure includes a scintillator that generates scintillation light in response to incident X-rays; a detection unit including a plurality of pixels each generating a pixel signal in response to the scintillation light incident thereon; and an output unit that generates X-ray two-dimensional projection data by using the pixel signals of the pixels. A pixel of the detection unit includes a plurality of subpixels that performs photoelectric conversion in response to the scintillation light; an AD conversion unit that applies AD conversion to outputs of the subpixels; and an adder that generates the pixel signal corresponding to the pixel by adding up outputs of the plurality of subpixels after the AD conversion. The present disclosure is applicable to an X-ray CT device and an X-ray FPD device.