1. An X-ray diagnosis apparatus comprising: an X-ray tube configured to generate X-rays to an examination target having a particular directionality; an X-ray detecting unit configured to detect X-rays penetrated through the examination target; an X-ray collimating unit including a plurality of aperture blades provided between the X-ray tube and the X-ray detecting unit for setting an effective X-ray irradiation region on the examination target by sliding and turning the plurality of aperture blades so that an effective X-ray irradiation is performed on the examination target depending upon the particular directionality; a driving unit configured to rotationally move the X-ray tube and the X-ray detecting unit; a region of interest setting unit configured to set up a region of interest on the examination target by executing a preliminary imaging mode for performing two 2D image reconstruction processes on the examination target along two imaging directions substantially orthogonal with each other, and designating region points on each of the two 2D reconstructed images; an X-ray aperture controlling unit configured to control the X-ray collimating unit so as to slide and turn the plurality of aperture blades in correspondence with the rotational movements, based on set up data of the region of interest and the two imaging directions, and an image data generating unit configured to generate image data for performing a 3D image reconstruction process based on each of position data of the region points designated on the two 2D reconstructed images and projection data acquired in correspondence with the rotational movements of the X-ray tube and the X-ray detecting unit.