1. A radiation tomographic imaging apparatus comprising: a radiation emitting device for scanning a subject to be imaged around a body axis direction of said subject to be imaged and emitting radiation to an imaging region in said subject to be imaged; a radiation detecting device for detecting said radiation passing through said subject to be imaged; and an image producing device for generating image data representing said imaging region based on said detected radiation, wherein said image producing device comprises an inter-imaging-plane filtering processing device for acquiring said image data for a plurality of planes generated corresponding to imaging planes that are a plurality of cross-sectional planes of said imaging region, and conducting filtering processing on said image data across said plurality of imaging planes.