1. An X-ray diagnosis apparatus comprising: a display-image creating unit that creates a display image from three-dimensional medical image data such that the display image of the three-dimensional medical image data substantially matches up with an anatomical structure on an acquired image by the X-ray diagnosis apparatus; a display-image changing unit that changes a display image so as to maintain consistency of an anatomical structure in accordance with change in an acquiring condition by the X-ray diagnosis apparatus; a display unit that displays a display image that is at least one of created and changed by at least one of the display-image creating unit and the display-image changing unit; a region-of-interest coordinate estimating unit that estimates a position of a region of interest as region-of-interest coordinates based on pixel information about three-dimensional medical image data present on a line connecting a focus point of an X-ray generating tube and a substantial center of a detector surface; an amount-of-control calculating unit that calculates an amount of control to be used for control of a certain device by using region-of-interest coordinates estimated by the region-of-interest coordinate estimating unit; and a control unit that controls the certain device in accordance with the amount of control calculated by the amount-of-control calculating unit.