An image processing apparatus for processing a radiation image output from a radiation detection means including a plurality of pixels, comprising: imaging protocol obtaining means for obtaining an imaging protocol that is imaging information for imaging a subject; dose obtaining means for obtaining dose information of radiation based on a feature amount of the radiation image and information obtained from the imaging protocol; body thickness information obtaining means for obtaining body thickness information of the subject based on the imaging protocol; and radiation quality information obtaining means for obtaining radiation quality information of the radiation based on the imaging protocol, wherein the dose obtaining means performs a region determination process of determining, based on a pixel value of the radiation image, a direct radiation region where radiation directly reaches the radiation detection means from radiation generation means and a non-direct radiation region other than the direct radiation region, wherein the dose obtaining means compares a reference value of a saturated pixel value with a pixel value in the direct radiation region, determines, if the pixel value in the direct radiation region is not smaller than the reference value, that the pixel value in the direct radiation region is saturated, and determines, if the pixel value in the direct radiation region is smaller than the reference value, that the pixel value in the direct radiation region is not saturated, and wherein if there is no direct radiation region or if the pixel value in the direct radiation region is saturated, the dose obtaining means obtains, as the dose information, one of a reaching dose of radiation having reached the radiation detection means and a pixel value corresponding to the reaching dose based on the feature amount of the radiation image and an attenuation property obtained based on the imaging protocol. imaging protocol obtaining means for obtaining an imaging protocol that is imaging information for imaging a subject; dose obtaining means for obtaining dose information of radiation based on a feature amount of the radiation image and information obtained from the imaging protocol; body thickness information obtaining means for obtaining body thickness information of the subject based on the imaging protocol; and radiation quality information obtaining means for obtaining radiation quality information of the radiation based on the imaging protocol, wherein the dose obtaining means performs a region determination process of determining, based on a pixel value of the radiation image, a direct radiation region where radiation directly reaches the radiation detection means from radiation generation means and a non-direct radiation region other than the direct radiation region, wherein the dose obtaining means compares a reference value of a saturated pixel value with a pixel value in the direct radiation region, determines, if the pixel value in the direct radiation region is not smaller than the reference value, that the pixel value in the direct radiation region is saturated, and determines, if the pixel value in the direct radiation region is smaller than the reference value, that the pixel value in the direct radiation region is not saturated, and wherein if there is no direct radiation region or if the pixel value in the direct radiation region is saturated, the dose obtaining means obtains, as the dose information, one of a reaching dose of radiation having reached the radiation detection means and a pixel value corresponding to the reaching dose based on the feature amount of the radiation image and an attenuation property obtained based on the imaging protocol.