1. A medical image diagnosis apparatus comprising: a lumen image generating unit that generates a lumen image depicting a shape of a lumen having a branch based on volume data that is three-dimensional medical image data; a running line generating unit that generates a plurality of running lines based on the shape of the lumen having the branch; an image synthesizing unit that generates a synthetic image by superimposing, on the lumen image, the plurality of the running lines indicating moving paths of a viewpoint in a virtual endoscopy image of the lumen having the branch; and a control unit that displays the synthetic image on a certain display unit, wherein the control unit controls the image synthesizing unit so as to perform depiction that distinguishes between a range of a running line along which a virtual endoscopy image is displayed and a range of a running line along which no virtual endoscopy image is displayed.