1. A medical image-processing apparatus that aligns volume data of two medical images, comprising: a setting part configured to set landmarks of medical images based on each set of volume data; a generating part configured to generate positional relationship information that indicates the positional relationships of said landmarks with regard to each set of volume data; a coordinating part configured to coordinate between the landmarks of two medical images that remain after eliminating some of the landmarks based on said positional relationship information; and an alignment part configured to align two sets of volume data based on said coordination of landmarks.