1. A radiation tomographic image generation apparatus, comprising: a radiation image storage means for storing a plurality of radiation images obtained from a radiation image detector by irradiating radiation to a subject on the radiation image detector from different directions by moving a radiation irradiation section, which is provided opposite to the radiation image detector, to a plurality of positions and irradiating the radiation from the radiation irradiation section in each of the positions; a tomographic image reconstruction means for reconstructing the plurality of images stored in the radiation image storage means to generate a tomographic image of the subject which is parallel to the detection surface of the radiation image detector; a first tomographic image generation means for generating a plurality of tomographic images with a first slice interval using the tomographic image reconstruction means; a region of interest detection means for detecting a region of interest from the tomographic images generated with the first slice interval; and a second tomographic image generation means for generating tomographic images with a second slice interval, which is smaller than the first slice interval, adjacent to the slice position of a tomographic image from which a region of interest is detected by the region of interest detection means using the tomographic image reconstruction means.