1. A radiation image processing apparatus that performs image processing on a radiation image based on scattered radiation generated by the subject, the radiation image being obtained without using an anti-scatter grid when capturing, the apparatus comprising: a receiver which receives the radiation image captured by applying radiation to a subject; a processor, which comprises: an area setting unit which sets a target area, and which adds another area different from the target area in the radiation image to the target area for performing the image processing of the target area in the radiation image; and an image processing unit that performs the image processing of the target area using the another area and the target area, wherein the image processing comprises obtaining a scattered radiation component using said another area and the target area, and reducing the scattered radiation in the target area based on the scattered radiation component, wherein the area setting unit further sets, in performing the image processing on the target area being processed, a small image area smaller than the processing target area for a processing target pixel in the processing target area, and wherein the image processing unit performs the image processing based on information of the small image area.