Various embodiments of the present invention suppress a reduction in the spatial resolution of a reconstruction image even if fan-para conversion is performed. Upon performing data conversion in which a rearrangement process and an interpolation process are performed on fan beam projection data P1 of a plurality of views to acquire equally-spaced parallel beam projection data P3 in which the intervals in a channel direction between radiation paths corresponding to respective data are equal, with respect to a plurality of view directions, the interval between the radiation paths in the channel direction is set more smaller than an interval considered to maximize the spatial resolution of the reconstructed image geometrically up to now, i.e., a reference interval ”d obtained by dividing the interval of arrangement of detecting elements in the channel direction by a projection enlargement rate at a detection surface of a detector at the time when an iso-center ISO is taken as a reference. Thus, the opportunity that pre-interpolation process data high in accuracy or data close thereto is used in back-projection increases, so that a reduction in the spatial resolution can be suppressed.
