An X-ray computed tomographic apparatus includes a gantry, a reconstructing portion, and a tube current value determining portion. The gantry acquires projection data of an arbitrary range in a body axial direction by continuously moving a tabletop on which a subject is laid down and by continuously rotating an X-ray tube about the subject. The reconstructing portion reconstructs image data from the acquired projection data according to reconstruction processing selected by an operator from plural types of reconstruction processing. The tube current value determining portion determines plural tube current values respectively corresponding to discrete, plural positions within the range, on the basis of the selected type of reconstruction processing and an image quality level specified or selected by the operator.