An image generating method is provided. The method includes performing a rearrangement process and an interpolation process on fan beam projection data, the fan beam projection data acquired by a scan that includes rotating a radiation source and a detector having a plurality of detecting elements arranged in a channel direction, wherein the interpolation process generates equally-spaced parallel beam projection data in which channel-direction intervals are equal therebetween, and wherein the interpolation process is performed with respect to a plurality of view directions. The method further includes performing a back-projection process on the equally-spaced parallel beam projection data to thereby reconstruct an image, wherein the channel-direction intervals between the equally-spaced parallel beam projection data are smaller than a reference interval obtained by dividing an interval between the detecting elements in the channel direction by a projection enlargement rate.
