According to one embodiment, an X-ray computed tomography apparatus includes an X-ray generation unit, an X-ray detection unit, a unit to reconstruct volume data for a reconstruction region having an operator-designated diameter based on projection data, a unit to generate interpolation data based on measurement data to complete projection data for end portions of the reconstruction region wherein the projection data required for reconstructing the volume data of a middle portion of the reconstruction region is acquired as the measurement data, and a unit to decide a width of the end portions based on the set radiation range along the tops longitudinal direction, reconstruction regions diameter, and objects imaging target portion.
