An image processing apparatus comprises a processing unit configured to performing energy subtraction processing using information concerning a plurality of attenuation rates corresponding to a plurality of radiation energies that are different from each other and are obtained by performing imaging in which an object is irradiated with radiation. The processing unit estimates attenuation information of a decomposition target material contained in the object using at least one image obtained by the energy subtraction processing, and generates an image concerning the decomposition target material using the attenuation information and the information concerning the plurality of attenuation rates.