A position information attaching unit (13) attaches, to each set of tomographic image data acquired from each scanning plane, position data for identifying a position of the tomographic image data within a three-dimensional region. A pre-memory (14) stores a plurality of sets of tomographic image data in a time-series order. A reconfiguration processing unit (20) uses the respective base images as division units to divide the plurality of sets of tomographic image data stored in the pre-memory (14) into a plurality of image groups. Then, data of a plurality of tomographic images which correspond to one another on a periodic basis are sequentially extracted from the respective image groups, and are stored in a post-memory (26) as one data block. A three-dimensional image-forming unit (28) forms a display image based on the plurality of sets of tomographic image data after reconfiguration stored in the post-memory (26) and while correlating each set of tomographic image data to a position within a display region identified by respective position data.