Radiation detector units provided with solid-state radiation detectors are supported on a supporting section, such that the radiation detector units are located at different distances from a radiation source and arrayed in a one-dimensional direction or two-dimensional directions. One of the radiation detector units is taken as a reference unit. Image size enlargement or reduction processing is performed on each of image signals outputted from the radiation detector units other than the reference unit and in accordance with a ratio between a distance from the radiation source to the reference unit and a distance from the radiation source to each of the radiation detector units other than the reference unit. Image composing processing is performed on the image signal outputted from the reference unit and processed image signals obtained from the image size enlargement or reduction processing.