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 a display image of 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; and 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.