1. An X-ray image diagnosis apparatus comprising: an imaging unit that supports an X-ray generation unit which emits an X ray to which a subject is exposed, and an X-ray detection unit which detects the X-ray that has passed through the subject, in such a way that the X-ray generation unit and the X-ray detection unit face each other and is possible to take an image of the subject placed on a top panel of a bed; a control unit that performs control in such a way that a step movement process of at least one of the imaging unit and top panel is carried out and images of the subject are taken at a plurality of stages; and an image processing unit that processes image data taken at a plurality of the stages, wherein the control unit sets a region of interest in an imaging area of the subject when an image is taken after a contrast medium is injected into the subject, measures a change of an image level in the region of interest to detect a flow of the contrast medium, and makes at least one of the imaging unit and top panel move to the next imaging stage on the basis of a result of the detection.