A radiation imaging apparatus includes a differential phase image producing section, a phase unwrapping section, a statistical operation section, and a correction processing section. The differential phase image producing section produces a differential phase image in which pixel values are wrapped into a predetermined range α. The phase unwrapping section performs a phase unwrapping process to the differential phase image. The statistical operation section obtains a mode from statistical operation of pixel values in each subregion segmented in the unwrapped differential phase image. Each subregion is a unit in which error caused by the phase unwrapping process is to be corrected. The correction processing section calculates, for each pixel, an integer “n” which allows a difference Δ between the mode and a pixel value of each pixel to satisfy nα−α/2≦Δ