An X-ray CT apparatus and an image reconstruction method are configured (i) to determine a movement phase to be used for generating diagnostic images with a small number of operations and (ii) to acquire diagnostic images in a short time while reducing a burden on an operator, such as when the target in scanning is a moving site. For example, an image processing device of an X-ray CT apparatus obtains movement information of a diagnostic site (such as the heart), determines phase selection positions, permits the operator to select an arbitrary movement phase based on the acquired movement information, and reconstructs selection images in a plurality of movement phases for each of the determined phase selection positions using scan data before presentation.