A pre-memory 14 stores a plurality of sets of tomographic image data in a time-series order. A virtual period setting unit 22 calculates a virtual period relating to an object based on the tomographic image data stored in the pre-memory 14. A base image searching unit 24 searches for base images from the tomographic image data using the virtual period. A division basis setting unit 26 sets division bases according to the base images within an image string constituted of tomographic image data. A reconfiguration processing unit 20 uses the respective base images as boundaries for the division to divide the tomographic image data stored in the pre-memory 14 into a plurality of image groups. Then, data blocks 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 28.