An X-ray diagnosis apparatus and a method for controlling an X-ray irradiation region that can appropriately narrow down an X-ray radiation aperture so as to fit a configuration of a region of interest during acquisition of X-ray projection data for reconstructing tomography images of an object.Based on a plurality of 2D image data acquired through a preliminarily X-ray imaging, a 3D region of interest is set up on an examination target portion having a strong directionality. X-ray imaging of the 3D region of interest is performed by sliding and rotating a plurality of aperture blades in an X-ray collimator based on a projected figure of the 3D region of interest along successively renewed imaging directions around a periphery of an object.