1. A radiation imaging apparatus comprising: a first radiation detection sensor configured to detect radiation irradiated from a first radiation generation unit via no grid; a second radiation detection sensor configured to detect radiation irradiated from a second radiation generation unit via a grid; a rotation unit configured to rotate each of the first radiation detection sensor and the second radiation detection sensor relative to a subject; a correction unit configured to acquire information on a scattered radiation distribution based on images respectively obtained from the first radiation detection sensor and the second radiation detection sensor at each rotation angle preliminarily determined by the rotation unit and to correct the image obtained from the second radiation detection sensor based on the information on the scattered radiation distribution so as to reduce influence of scattered radiation thereon; and a reconstruction unit configured to perform reconstruction processing based on the image corrected by the correction unit.