An image generating method comprising the steps: a data conversion step for performing a rearrangement process and an interpolation process on fan beam projection data of a plurality of views acquired by a scan for rotating a radiation source and a detector having a plurality of detecting elements arranged in a channel direction about a target to thereby acquire equally-spaced parallel beam projection data in which channel-direction intervals are equal, with respect to a plurality of view directions; and an image reconstruction step for performing a back-projection process on the acquired equally-spaced parallel beam projection data to thereby reconstruct an image, wherein the interval between the equally-spaced parallel beam projection data in the channel direction is smaller than a reference interval obtained by dividing the interval of arrangement of the detecting elements in the channel direction by a projection enlargement rate at a detection surface of the detector at the time that the center of rotation of each of the radiation source and the detector is taken as a reference; wherein, near the center of rotation, positions of radiation paths of the equally-spaced parallel beam projection data in the channel direction overlap with positions of radiation paths of unequally-spaced parallel beam projection data lying next to each other in the channel direction; wherein the unequally-spaced parallel beam projection data is generated by the rearrangement process on the fan beam projection data for a plurality of views; and wherein the interval between the equally-spaced parallel beam projection data in the channel direction is 1/N, where N of the reference interval is any integer ranging 2 to 4. a data conversion step for performing a rearrangement process and an interpolation process on fan beam projection data of a plurality of views acquired by a scan for rotating a radiation source and a detector having a plurality of detecting elements arranged in a channel direction about a target to thereby acquire equally-spaced parallel beam projection data in which channel-direction intervals are equal, with respect to a plurality of view directions; and an image reconstruction step for performing a back-projection process on the acquired equally-spaced parallel beam projection data to thereby reconstruct an image, wherein the interval between the equally-spaced parallel beam projection data in the channel direction is smaller than a reference interval obtained by dividing the interval of arrangement of the detecting elements in the channel direction by a projection enlargement rate at a detection surface of the detector at the time that the center of rotation of each of the radiation source and the detector is taken as a reference; wherein, near the center of rotation, positions of radiation paths of the equally-spaced parallel beam projection data in the channel direction overlap with positions of radiation paths of unequally-spaced parallel beam projection data lying next to each other in the channel direction; wherein the unequally-spaced parallel beam projection data is generated by the rearrangement process on the fan beam projection data for a plurality of views; and wherein the interval between the equally-spaced parallel beam projection data in the channel direction is 1/N, where N of the reference interval is any integer ranging 2 to 4.