1. An X-ray diagnosis apparatus comprising: an X-ray tube; an imaging system which detects X-rays emitted from said X-ray tube and transmitted through an object to be examined, and generates X-ray image data; an arm which supports said X-ray tube and said imaging system; an arm support mechanism which rotatably and movably supports said arm; a bed which holds the object between said X-ray tube and said imaging system; a three-dimensional image generating unit which generates three-dimensional image data from volume data concerning the object; a display unit which displays the three-dimensional image data; an input device which designates an interest point on the displayed three-dimensional image data; and a controller which controls at least one of said arm support mechanism and said bed, such that the center of the X-ray image data generated by said imaging system is positioned on a portion of the object which substantially corresponds to the designated interest point.