Radiation imaging apparatus, and calibration method for photon counting type detector

A radiation imaging apparatus provided with a photon counting type detector for outputting an electric signal corresponding to energy of an incident radiation photon includes a measured value recording unit for measuring an attenuation value in the presence of a known calibration member while changing a threshold value of a detector output of the photon counting type detector and recording a measured value of the attenuation value for each threshold value of the detector output, a theoretical value calculation unit for calculating a theoretical value of the attenuation value in the presence of the calibration member with respect to multiple energies, a calibration information acquisition unit for acquiring a relation between the threshold value and the energy as calibration information by performing collation between the measured value and the theoretical value, and a calibration processing unit for converting the electric signal outputted from the photon counting type detector into energy.