A radiation imaging apparatus includes: a detection unit configured to obtain measurement information based on a detection result of radiation irradiated based on a constant tube voltage an obtaining unit configured to obtain second measurement information of the radiation based on a moment of the measurement information obtained by detecting the radiation multiple times an energy determination unit configured to determine a plurality of energies for approximating an energy distribution of the radiation and a calculation unit configured to calculate photon counts corresponding to the plurality of energies based on the second measurement information.
