There is provided a radiation detector that appropriately corrects an offset within a minute read cell without increasing area while achieving high-speed measurement at a high counting rate. A radiation detector 100 having a plurality of single-photon-counting imaging cells includes, for each imaging cell, a photodiode 3 which is applied with a reverse bias voltage and generates a current signal in response to incidence of radiation, a previous-stage DA converter d1 configured to correct an input signal based on the current signal generated by the photodiode 3, an amplifier k2 configured to amplify the signal corrected by the previous-stage DA converter d1, a subsequent-stage DA converter d2 configured to correct a charge signal amplified by the amplifier k2, a wave height discriminator 9 configured to discriminate output signals based on the signal corrected by the subsequent-stage DA converter d2, and a counter 10 configured to count the discriminated signals.