In order to provide a data processing method and the like capable of suppressing high-frequency errors such as moiré using data uniformly by presuming that adjacent pixels and beams overlap and performing calculation in a back projection process or a forward projection process for reconstructing images, the image processing device 122 sets a pixel size wider than a pixel interval, performs the back projection process or the forward projection process for calculating an interpolation value to be assigned to the pixels or the beams using a size-dependent weight (pixel window) according to an overlap amount of the adjacent pixels, sets a beam size wider than a beam interval, and then performs the back projection process or the forward projection process for calculating an interpolation value to be assigned to the pixels or the beams using a size-dependent weight (beam window) according to an overlap amount of the adjacent beams.
