1. A method of reconstructing tomograms, in which at least one X-ray spectrum is radiated to a target comprising at least one material in order to reconstruct the tomograms of the target from an X-ray transmitted through the target, the method comprising: receiving transmission image data that is measured by detecting the X-ray transmitted through the target; obtaining reconstruction information of the target from the measured transmission image data in consideration of a fact that the X-ray has a polychromatic X-ray spectrum; and generating the tomograms of the target from the obtained reconstruction information.