The accuracy of combining positions of elongated images is improved at low cost, in a radiation imaging apparatus for generating elongated images having dimensions greater than a detectable range of a radiation image detecting means. A laser source is utilized. Displacement measuring means for measuring distances to targets by receiving a laser beam reflected by the subjects is provided. Positions that correspond to the ends of images in the movement direction of the radiation image detecting means are scanned in the direction perpendicular to the movement direction with the laser beam at each imaging operation. The displacement measuring means measures the positions of the ends of subjects in the laser scanning direction by receiving the laser beam reflected during scanning. An image processing means matches the combining positions of radiation images such that the ends of the subjects measured during each imaging operation are matched, and generates the elongated image.