An object is to provide intensity information and energy information while reducing processing load and power consumption. In a radiation detector, a radiation detection element, in which a plurality of pixels each configured to generate an electric charge corresponding to energy of X-rays penetrating a subject is two-dimensionally arranged, and a plurality of read circuits each configured to output an intensity signal of transmitted X-rays based on the electric charge generated by each of the plurality of pixels are stacked with each other, and some read circuits thinned out from a plurality of read circuits each generate a spectral signal related to a spectrum of a transmitted X-ray based on the electric charge and output the spectral signal.