1. An X-ray diagnostic apparatus comprising: a memory which stores a plurality of images, wherein the plurality of images are images acquired in a plurality of projection directions by rotation around an object to be examined; a designating section which designates a region of interest on at least one of the plurality of images acquired in a predetermined projection direction on the basis of an input from an operator; a position estimating section which estimates corresponding areas in each projection direction, which correspond to the region of interest in each projection direction, on the remaining images of the plurality of images; a transformation section which transforms the plurality of images so as to locate the region of interest and the respective corresponding areas at substantially a same display position; and a display section which after transformation by said transformation section sequentially displays the transformed images with display positions thereof adjusted such that an operator is free from moving an eyepoint to observe the transformed images.