1. A 3D image processing apparatus comprising: a storing unit configured to store data of a plurality of mask images corresponding to a plurality of projection directions associated with an object to be examined, and data of a plurality of contrast images corresponding to the plurality of projection directions associated with the object; a subtracting unit configured to generate data of a plurality of subtraction images by subtracting the plurality of mask images from the plurality of contrast images; a reconstruction unit configured to reconstruct first volume data from the plurality of mask images and reconstructs second volume data from the plurality of subtraction images; an image processing unit configured to generate data of a first 3D image representing a bone structure and/or a soft tissue structure from the first volume data, and generates data of a second 3D image representing a contrasted blood vessel from the second volume data; an image synthesizing unit configured to generate data of a synthetic image by synthesizing the first 3D image with the second 3D image; and a displaying unit configured to display the synthetic image.